1. A sustained release drug delivery system comprising: an inner drug core comprising a therapeutically effective amount of an agent effective in obtaining a desired local or systemic physiological or pharmacological effect; an inner tube impermeable to the passage of said agent, said inner tube having first and second ends and covering at least a portion of said inner drug core, said inner tube sized and formed of a material so that said inner tube is dimensionally stable to accept said drug core without changing shape; an impermeable member positioned at said inner tube first end, said impermeable member preventing passage of said agent out of said drug core through said inner tube first end; and a permeable member positioned at said inner tube second end, said permeable member allowing diffusion of said agent out of said drug core through said inner tube second end. 2. A sustained release drug delivery system in accordance with claim 1, wherein said inner tube is a polymer or a metal. 3. A sustained release drug delivery system in accordance with claim 1, wherein said impermeable member comprises an impermeable cap abutting said inner tube first end. 4. A sustained release drug delivery system in accordance with claim 1, further comprising a permeable outer layer surrounding said inner tube, and wherein said permeable member comprises a portion of said permeable outer layer. 5. A sustained release drug delivery system in accordance with claim 4, further comprising a hole through said impermeable inner tube communicating said drug core with said permeable outer layer. 6. A sustained release drug delivery system in accordance with claim 1, further comprising an impermeable outer layer surrounding said inner tube, and wherein said impermeable member comprises a portion of said impermeable outer layer. 7. A sustained release drug delivery system in accordance with claim 6, wherein said permeable member comprises a permeable plug abutting said inner tube second end. 8. A sustained release drug delivery system in accordance with claim 7, where in said permeable plug has a radial exterior surface and an end surface opposite said drug core, and said impermeable outer layer covers at least part of said radial exterior surface and at least a part of said plug end surface. 9. A sustained release drug delivery system in accordance with claim 7, further comprising a port in said impermeable outer layer positioned to allow agent to diffuse out of said drug core, through said plug, through said port, and out of said device. 10. A sustained release drug delivery system in accordance with claim 9, wherein said port is formed in said impermeable outer layer immediately adjacent to a surface of said plug selected from the group consisting of said plug end surface, said plug radial surface, and both. 11. A sustained release drug delivery system in accordance with claim 9, wherein said port is formed in said impermeable outer layer immediately adjacent said plug radial surface, and wherein said port comprises a plurality of openings formed in said impermeable outer layer immediately adjacent said plug radial surface. 12. A sustained release drug delivery system in accordance with claim 7, wherein said impermeable outer layer extends along and covers said plug radial surface and terminates at said plug end surface. 13. A sustained release drug delivery system in accordance with claim 1, wherein said effective agent is fluocinolone acetonide. 14. A sustained release drug delivery system in accordance with claim 1, wherein said effective agent is nimodipine. 15. A sustained release drug delivery system in accordance with claim 1, wherein said effective agent is a steroid. 16. A sustained release drug delivery system in accordance with claim 1, wherein said effective agent is a neuroprotectant. 17. A sustained release drug delivery system in accordance with claim 1, wherein said impermeable inner tube is formed of a material which impedes the passage of eroding agents into said inner drug core when said system is exposed to said eroding agents. 18. A use of the sustained release drug delivery system in accordance with claim 1 for treating a mammalian organism to obtain a desired local or systemic physiological or pharmacological effect. 19. A use of the sustained release drug delivery system in accordance with claim 1 for treating a mammalian organism for ocular edema, ocular neovascularization, ocular edema, or ocular inflammation, said drug delivery system drug core comprising a therapeutically effective amount of a steroid effective to obtain a desired local or systemic physiological or pharmacological effect. 20. A use in accordance with claim 19, wherein said steroid is corticosteroid. 21. A use in accordance with claim 20, wherein said corticosteroid is fluocinolone acetonide. 22. A use of the sustained release drug delivery system in accordance with claim 1 for providing controlled and sustained administration of an agent effective in obtaining a desired local or systemic physiological or pharmacological effect comprising: inserting the sustained release drug delivery system at a desired location. 23. A use in accordance with claim 22, wherein said inserting step comprises injecting said system at a desired location. 24. A use in accordance with claim 22, wherein said inserting step comprises surgically implanting said system at a desired location. 25. A use in accordance with claim 22, wherein said inserting step comprises inserting said system in a location selected from the group consisting of the vitreous of the eye, under the retina, and onto the sclera. 26. A use in accordance with claim 22, wherein said effective agent is a corticosteroid. 27. A use in accordance with claim 26, wherein said corticosteroid is fluocinolone acetonide. 28. A use in accordance with claim 22, wherein said effective agent is a neuroprotectant. 29. A use in accordance with claim 28, wherein said neuroprotectant is nimodipine. 30. A method of manufacturing a sustained drug delivery system, comprising positioning a drug core in a tube, said drug core containing a therapeutically effective amount of an active agent; and positioning an end member to said tube to form a closed-end tube, said end member selected from the group consisting of an impermeable cap and a permeable plug. 31. A method in accordance with claim 30, further comprising forming an outer layer around a portion of said tube, said outer layer formed of a material selected from the group consisting of a permeable material and an impermeable material. 32. A method in accordance with claim 30, wherein said positioning an end member comprises joining said end member to a length of said tube to form a vessel-shaped member. 33. A method in accordance with claim 30, wherein said, positioning a drug core comprises positioning said drug core in a length of tube which is sized and formed of a material so that said length of tube is dimensionally stable during said positioning. 34. A method in accordance with claim 32, wherein said joining step comprises abutting said end member against a first end of said length of tube, and leaving a second end of said length of tube uncovered. 35. A method in accordance with claim 32, wherein said joining step comprises joining an impermeable cap to said length of tube, and wherein said step of forming an outer layer comprises forming an outer layer of a permeable material. 36. A method in accordance with claim 32, wherein said-joining step comprises the step of joining a permeable plug to said length of tube, and wherein said step of forming an outer layer comprises forming an outer layer of an impermeable material. 37. A method in accordance with claim 36, further comprising the step of forming a port in said impermeable outer layer immediately adjacent to said permeable plug. 38. A method in accordance with claim 37, wherein said step of forming a port further comprises forming a port immediately adjacent to an end surface of said plug opposite said drug core. 39. A method in accordance with claim 37, wherein said step of forming a port further comprises forming a port immediately adjacent to a radial surface of said plug. 40. A method in accordance with claim 37, wherein said step of forming a port further comprises forming a plurality of ports. 41. A sustained release drug delivery system comprising: a drug reservoir comprising a therapeutically effective amount of an agent; an inner tube having first and second ends and covering at least a portion of said drug reservoir, said inner tube formed of a material that retains structural integrity during drug diffusion; and an outer layer covering at least a portion of said drug reservoir and/or inner tube. 42. A method of manufacturing a sustained drug delivery system, comprising positioning a drug core in a tube, said drug core containing a therapeutically effective amount of an active agent; and cross-sectionally cutting the tube into sections. 43. A method in accordance with claim 42, further comprising forming an outer layer around a portion of a section, said outer layer formed of a material selected from a permeable material and an impermeable material. 44. A method in accordance with claim 42, wherein positioning a drug core comprises positioning a said drug core in a length of tube which is sized and formed of a material so that said length of tube is dimensionally stable during said positioning. 45. A sustained release drug delivery system in accordance with claim 41, wherein said inner tube is permeable to passage of the agent. 46. A sustained release drug delivery system in accordance with claim 41, wherein said inner tube is impermeable to passage of the agent. 47. A sustained release drug delivery system in accordance with claim 41, wherein said inner - tube includes at least one port or hole. 48. A sustained release drug delivery system in accordance with claim 45, wherein said inner 'tube