I've been experiencing the issue where if a single user is logged into XP, the trackpoint scroll feature works flawlessly, BUT, if you use the XP switch user function and have 2 people logged in at the same time, the trackpoint scroll feature breaks down and doesn't work right.
This is what I've found (short of re-booting the system): User1 logged on --> Switch User to User2, the scroll feature will work, BUT if you Switch User back to User1 the trackpoint scroll doesn't work anymore So, to get it to work right for User1 again, Switch User back to User2 and Logoff --> Log back in with User1 and should work again.
I've done all the driver uninstall/re-install excercises and have tried the native synaptic drivers too.... This just seems to be the way this works (unfortunately).
Ironically, my old T30 had seemingly the same hardware, but I never had this problem with it... it was seemless when Switching Users. Funny, I bought a ThinkPad T because I love the trackpoint... I wish they would get it to work right