USB 2 External Hard DIsk support

Help - we have 4 Optiplex G260 systems (P4 1.8 GHZ) where we need to transfer large files (>5 GB) over USB2 port to a portable USB2 hard disk, in a windows These portable hard disks have been use in dozens of systems without problems. We are using windows 2000 sp4. Only our Dells are having problems. The portable hard drive will be recognized fine and the file transfer will take place and give a time remaining of say 3 min - after it almost reaches zero - it will read an astronomically high figure 1992345234223450 minutes say, and it will stay there and never finish copying the file. if you cancel the file will not be copied. Ive tried installing PCI USB 2 cards in these Optiplex machines and the same thing happens. the System devices show that Intel enhanced USB controller and USB 2.0 Root hub is working. I dont think its the disk unit as these work fine in Many systems.

These machines use the latest Bioses and the website say that the Optiplex G260 support usb 2. I could not get any tech support over the phone because the dell guy said its an external device and not covered by any warranties. ( so much for the great interns at dell). We also experienced the same thing with a Dell PowerEdge 500 SC server with windows 2000 server.Has anyone ever seen this issue. I think i have all the right drivers and there are no yellow x's in the device manager.