Consider whether you will be hosting your own Web services or e-mail, or if they are or will be located at an ISP or colocated at a secure site. This is important to your Internet connectivity needs and in deciding which platforms you may need to run various services. Speaking of security, it is easy to be lax about what gets connected to the Internet. Do not scrimp on security and virus-protection software, proxy servers, firewalls, routers, and switches. Keep your back-office systems off the Internet at all costs.
Planning is everything.
Windows 2000 may be a bit too new and complex to scale with, while NetWare and Linux hold their own. Everything depends on what you need now and may need later. If you do not need a Microsoft solution for servers, then NetWare, Linux, or OS X will do just fine. Why pay more than 5 cents a minute for long distance.