Hi people - many apologies for not popping back in earlier, although I did try a few times over the last few days and got a "cgi-script" error when acccessing this forum.
First - thanks for all your help so far, I've read through all the threads since my last visit and have tried a couple of your ideas.
What I did in the end (due to time constraints) that seems to have sorted it all out was and old but sometimes effective method: I removed all kix32.exe and *.kix scripts from all my domain controllers and from the XP workstations, removed the group policy object from the A.D, deleted all copies of C:\Windows\prefetch\kix* files from my XP workstations. THEN started again, re-created GPO in AD, created a shutdown script in the GPO (batch file) that copied the latest kix32.exe and logon.kix files a newly created C:\kix folder of my XP workstations, setup configured the scripts to run locally on the workstations and to be called directly from the GPO (no batch file).

Since then, the scripts seem to be working OK. What is still annoying, though, is that I don't really know why they behaved the way they did in the first place? I'm sure we've all been there before, where ANYTHING to get a problem resolved is a welcomed relief, even though you're still not sure what it was that fixed the problem.

I will continue to try and track the seemingly obscure source of my issue so that others may not feel the same frustration and will post any updates I think are relevant.

I have a horrible feeling that my issue may only be temporarily resolved.