USB Devices keep getting disconnected

I running into constant problems with two of my USB devices. They are a 3Com HomeConnect video camera and a Lexar Memory Stick reader. I constantly get the "Lost connection with video device" or "Failure of I/O device, USB device not recognized". These may not be the exact error messages but they are something to that effect. It can happen at any time. One minute into use or 2 hours. I cannot detect a pattern. I recently lost some priceless pictures off my Memory Stick when I was trying to transfer them to my computer via the Lexar Memory Stick reader.

I'm using the latest WindowsXP drivers supplied by 3Com and Lexar

Dell had me to turn the USB Emulation to "On" in the BIOs settings but this did not help.

WindowsXP
Dell Dimension 8100
1.5 GHZ
512 MB of Ram

I'd appreciate any help you can give.

Thanks,