I have several external USB hard drives (2 TB each) that I use to back up files - they all worked wonderfully on my five year old Win XP machine.
I just got a brand new Win 7 machine and whenever I plug any of the drives into any of the USB ports, the system slows to an unusable crawl. It takes minutes to navigate screens. Also, the hard drive activity is maxed out. However, using task manager there are no processes sucking either cpu or ram.