Last week, when we installed SQL Server 2000 on Windows 2003, we got the same problem. Please look at the Microsoft web link below first.

http://support.microsoft.com/default.aspx?scid=kb;en-us;319349

But we didn't follow the doc. We just remove SQL Server, then make sure uncheck the Force Protocol Encryption option before you reinstall SQL. Hopefully can give you an idea to figure out your problem.

Ray