We have Windows XP client and NT4.0 SP6a servers. Logon.bat is as below:

%0\..\KIX32.EXE KICK.SCR
EXIT

Kick.scr calls something.kix depending on group membership.
It works ok, even on dialup. We only have 2 machines running the new OS. One is a Celeron 766 with 64MB and the other is a 1.4GHz Pentium with 128MB.
I've not had to do anything different to make it the scripts work for XP. I can enclose more scripts if necessary. I'd like to get to the bottom of this. Sounds a bit flaky to me, so we might have problems soon.