Yeah, the usb ports can only supply 500mA (iirc) no matter how much juice your psu can supply. You may be exceeding that, there used to be a bar graph so you could tell what sort of power you were using in 98SE. In XPx64 it's a little different...
Press Windows+Break.
Click Hardware tab, Device Manager, expand the USB devices.
Double click on each of the USB Root Hubs in turn, and click the Power tab.
To fix it, you'll need to plug the device drawing too much power into a different usb port. On the back of your PC, the ports are bunched together in pairs. Usually each pair represents a Root Hub. Distribute your devices across different root hubs and you should be all set. If you have too many devices, pair a power hungry device (such as an Xbox controller with a mouse, or a G15 with a phone that's rarely plugged in). If you still have problems, you need a powered Hub. That is, a hub which has a separate power pack, these can usually supply 1500mA iirc.
