USB Transfer Rate with kvm-77

Hello,

I'm currently testing Windows XP in a Linux host. I works well except the USB transfer rate. Printers and USB Pen Drives can be connected and get detected (I added host:auto...). My System only supports USB 1.1, the transfer rate in plain linux is okay. In the Guest Windows, the transfer rate is horribly slow! The transfer rate is ~ 2MB per Minute! This is far below the slowest defined USB transfer rates (1,5MBit / sec!). The system is nearly idle (in linux and windows) during the transfer. What could be the reason for that? I tested it also on a USB 2.0 system, same effect, but additionally the printers cause bluescreens within Windows :-)
I need some ideas where to start investigating. I tested several USB Pen Drives (USB 2.0 capable), a USB DVD ROM Drive and two printers of different manufacturers (HP, Canon). All at the same transfer rate :-(
It seems that there is a performance gap - but where?

Thanks a lot!

Best regards,

Erik