Problem with RegVac on WinXP Pro SP2?

Good evening!

I discovered a trojan on my machine which my free anti-virus program didn't pick up, although some of the standard anti-virus sites list it.  Since it didn't have an uninstall program, I decided to remove it by deleting the relevant files, using RegVac to clean the registry, and using msconfig to remove an entry it had added to win.ini.  I've done cleanups in that way before.  I first made a backup of the registry and some other odds and ends using WinRescue XP (I'm running XP Pro SP2.)

After removing the files and the win.ini entry, rebooting after each action, everything was fine.  I then ran Classes Vac from RegVac 4.02.12.  (I also did searches using Software Vac and Bad Link Vac, but I didn't find anything worth deleting.)  I rebooted after using RegVac, seemed to enter Windows OK, but couldn't connect to the net or to my router.  Windows showed the connection as "connected", but no data were being passed either way.  There were some other problems with the Windows networking setup, but I don't remember the details.  I then entered the RegVac Undo window.  I couldn't get that day's .reg file to show anything in the main window, and Windows showed it has having 0 bytes.

I restored the registry using WinRescue, rebooted, and everything worked fine.

I then tried to use an old version of RegVac which I have, file modified August 2003.  I could get expert mode to display properly at all.  Novice mode did remove some junk, apparently using both Classes Vac and Software Vac.  Everything seems to be fine now.

My questions are:
1. Why did 4.02.12 apparently delete from the registry and damage my registry without putting anything into the .reg file?  Is it safe to use this version on WinXP Pro SP2?
2. Why can't I use my old version of RegVac with WinXP?  Is it simply too old to be compatible?

Thanks.
C.