It looks like the final solution from where you are would be to:
1: Uninstall the RealTek drivers (under delete program)
2: Delete audio components (from the device manager)
4: Locate the RealTek driver on your or Mac Install CD (or from a download from RealTek's site) (BOOTCAMP > Drivers > RealTekSetup)
5: Right-click on the installer and select "troubleshoot compatibility"
6: Wait for it to finish "detecting issues"
7: Select "this program worked on an earlier version of Windows, but won't install or display correctly now"
8: Select Windows Vista or Windows XP
9: Wait for it to finish "resolving issues", the installer will start
Hopefully this will have you up and running.