Building on what Brad suggests, try running the same simple tests as login scripts (test user account pointing to the test script for login) as well as interactively after logon.
FYI - I just worked with a client in Australia where scripts failed during logon but worked after, only on a handful of systems. Something corrupt in the workstation config (XP SP3 as well) caused the environment to become corrupt/empty only during login, causing the script to fail to run properly and throw errors. There weren't enough systems failing to bother diagnosing further and the workstations were re-imaged, so I can't offer any real solution. It was a strange problem and it would be good to rule out.
Glenn
_________________________
Actually I
am a Rocket Scientist!
