Computers built by me. Abit vt7 running Windows XP. USB 2.0 ports only work at USB 1.1 speeds. The only computer that seems to work right is an almost all usb/firewire computer that seems to be the fastest. Nothing helpful from Abits website. Reloaded drivers several times. Should be a test you could run with a null usb cable between the ports or two computers. There is the usual conflicts under System Information. Is it because all the ports use IRQ 21 and each need there own IRQ?

Computers & Internet - Abit - VT7 Motherboard