Rollback to XI R2 SP2

Hi.

I have CR XI R2 SP2 (full build) on a XP machine. I applied SP 3 on it a few days back. Now, after I have removed SP3, I still see my version number to be the same as it was after installing SP3. This indicates that SP3 has not been removed completely. Can you please provide me with further guidelines for a COMPLETE uninstallation of SP3? Are there any keys in the registry that need to be modified/deleted?

Thanks,

Alok.