I had a few similiar issues also. I resolved them by doing some serious "hacks" on XP (Pro)
From memory, they involved making the XP run like 2K
-disabled quick user switching
-provided a proper login screen at startup
- demoted browser status to prevent w/s attempting to become a master browser
Many of these "hacks" can be found at
www.sanx.org (and I am sure other places also...)
HTH - Post you final settings back to the list.
Peter