I replied to this in another post somewhere, but here we go:
What system are you running it on? Linux, Windows, etc...
I've done it with a Red Hat Linux box and to get it to work was an incredible pain. I won't go into detail unless you have a linux box because it's going to take me time to get my notes and post them, but the basic idea is this: MSSQL 2000 won't work with PHP inherently. On a Linux box I had to get the Sybase extensions for SQL and then install them and go through the whole setup process of that. And then I had to recompile Apache and then recompile PHP inorder to support the extension module created in the process. After that though, the connection to the MS SQL 2000 server runs really nice.
Hopefully that can help you since I also know that there's FreeTDS instead of Sybase extensions that can possibly work to make the PHP work with the MSSQL 2000 server.