I think smah has the right idea. It is a BIOS issue. I had a similar problem on a client machine, and created the following rule:
. If there is a legacy USB setting in the BIOS, enable it if you use USB mice or keyboard;
. If there is a legacy USB setting already enabled and you have mice or keyboard issues, disable it.
The Microsoft USB products seem to like having the BIOS setting enabled; the Logitech products seem better (not always) with the BIOS setting disabled.
Note as well that if you are using an USB-2-PS/2 adapter for the mouse, toss it in the trash can. This is just problematic under XP.