USB 2.0 speed

[Alexandros Papadopoulos <apapadop@alumni.carnegiemellon.edu>]

I have an external HDD case, that is USB 2.0 certified. When I boot my 
machine with KNOPPIX and have the USB case plugged, I get fast transfer 
rates to my external disk (10MB/sec or so).

When I boot my regual installation of Debian (sarge), with both kernels 
2.4.25 and 2.6.8 (installed via apt-get), the same modules are loaded 
(uhci-hcd and friends), but the system can only exchange data with the 
external drive VERY slowly (less than 500kb/sec).

usbview shows me at that time that the external USB device (correctly) 
advertises speeds of up to 480Mbps, but actual file transfers are 
extremely slow.

Anyone have any idea on how to troubleshoot this?

Thanks

-A