Hi again, just been doing bit of research for you & think I can solve your problem!
Most mobos with USBv1.1, have single circuit powering ALL usb ports. Therefore power is split between them which limits all connected usb devices to theoretical max of 12mbps & 0.5A in total.
(Bear in mind that USB modems/printers etc draw a particularly high current.)
Non-Intel chipsets, (I believe yours is VIA), also have design flaw with USB controller that means they are not able to ramp signal voltages fast enough under load.
XP in particular also has many compatibility issues with USB, if that is the OS you are using.
Possible solutions are :
1) Only use one USB device at a time & disconnect others
2) Use a powered USB external hub & connect devices to that
3) Use shorter USB cables (I suspect this measure alone will not be sufficient)
4) Use a PCI USB card instead.
Hope this all helps!