try this
go to start ->run
type msiexec /unregserver
and then
type msiexec /regserver
try running the installation..hope this helps
if not try this
Restart in safe mode your PC go to c:\windows\system32 and rename msi.dll,msiexec.exe and msihnd.dll you can chance the ext .dll to .old
Then restart windows to normal mode and reinstal windows installer and try the installation
( you can find the windows installer in CD1 of symante endpoint protection )
Regards
Rafeeq