Make sure you delete these folders
C:\Program Files\Symantec
C:\Program Files\Common Files\Symantec Shared
C:\Documents and Settings\All Users\Application Data\Symantec
Then reboot the 2003 server.
Then run the install.
If it still fails then
go to start - run -%temp%\SEP_INST.log
look for
return value 3 and copy the 10 lines above return value 3 and post it over here