It has been noted by quite a few users on these forums that the upgrade path from 4 to 5 isn't working anything like it should. It has been recommended that everybody uninstalls version 4 completely, using the cleaner tool if necessary, then installs version 5 from scratch.
My install of version 5 with xp home sp3 is working great.
Can't remember what the cleaner tool is called, I'm sure somebody will chip in...
regards, Gizbar.