Jen,
You have a big problem with your computer set up in the office. It sounds like you have a mixed environment of different products, installs of software, etc. Like Bert said you need to sit down and figure out what you want to do with your office network. You are better off to set up a client-server set up rather than a peer to peer. I would also recommend you seek professional IT help or spend a lot of time learning IT stuff.
If you have the SBS 2003 software your easily transfer that software and license to another computer. You can purchase an inexpensive server from Dell or HP without the OS and just install it.
You can attach Windows 2000 clients to the SBS 2003. It may be a little more work but can be done.
Good Luck,
Geoff
