Symantec Admits Fault in XP SP3 Registry Issues
"After a lot of testing, we've reproduced a number of different cases where applying the XP SP3 upgrade adds additional registry keys within already-existing Symantec registry keys," said Anschultz. "We have determined that the SymProtect feature is involved, though this issue is not exclusive to Symantec customers. To help prevent this issue from occurring, you should disable SymProtect prior to installing the Windows XP SP3 upgrade."
Symantec also noted they would post a standalone tool later. However, a later post on the same thread seemed to indicate a similar issue with the installation of Vista SP1, although that same Symantec manager noted they hadn't noted such reports previously.