You need an agent to tell you if you're stepping into a hole by signing that contract. Don't believe anyone who tells you that your book won't sell unless an agent is representing it. Finally, never under any circumstances should you pay anyone claiming to be an agent, editor, or publisher to represent, edit, or publish your work. You're the author. They pay you.
Agents are always a hot topic on The Rumor Mill .
For more information, we suggest a quick trip to Dave Kuzminski's excellent Preditors and Editors . SFWA is also an excellent resource.