Don't bother yoursef with USB Mice - They use more resorces then PS/2 (CPU and memory for USB interface support)
They don't work in Dos/Safe-mode...
They use an USB port which can be used for other more important things like printer/scanner
They leave the PS/2 mouse port unused - you can't use it for enything else
PS/2 can be set to up to 200Hz refresh sycle while USB is limited to 120Hz - if you need precision (graphics...) from your mouse - use PS/2, if not... still use PS/2
