If your MDAC on XP gets corrupted you cannot just download MDAC 2.8 RTM and re-install it.
XP will not allow this. XP will complain that it is already installed.

This is how to repair MDAC 2.8 on WinXP with SP2 installed

Right click on the file c:\windows\inf\mdac.inf, then select install.
When prompted for a location, Choose c:\windows\servicepackfiles\i386 then XP will ask for the cd for XP, Use the original CD or the location c:\i386. This will re-install the MDAC that came with Windows XP, SP2.