External Hard Drive -- too much power for my USB... I purchased a Western Digital My Passport

Question

I purchased a Western Digital My Passport Essential Portable hard drive (320 GB) (model WD3200ME-01; order WDME3200TN). When I insert the USB cord into my 600M Inspiron Dell computer, the computer states the USB device has exceeded the power limits of its hub port. What does this mean and how do I fix it? Do I have to buy another type of external hard drive? Thank you.