When upgrading from Windows 2000 to 2003, the oledb32.dll incorrectly uses an old version that will disable your ability to use odbc and ole connections.
You can't reinstall mdac 2.8 since that's part of the new OS, but you can do the following to resolve it.
Copy it from an existing MDAC 2.8 machine to C:\WINNT\system32\dllcache and C:\Program Files\Common Files\System\OLE DB (in that order) on the server and tehn reboot it.