While attempting to add a datasource from within BI Development Studio, I
cannot enumerate databases for any server. If I type the database name and
click 'Test Connection', I get the error message:

Test connection failed because of an error in initializing provider.
[DBNETLIB][ConnectionOpen (PreLoginHandshake()).]General network error. Check
your network documentation.

This happens for the Native Client, OLEDB Provider, and the .Net provider.

SQL Management Studio has no problem connecting to any of the servers from
this machine.

This is a clean install of WinXP, followed by SP2, then Office 2003
Standard, then SQL2005 workstation components.