A lot of people dont know these exist and they are cheap and handy.
It allows you to connect a normal hard disk or cd/dvd rom drive through your usb port.
Fantastic for older laptops with small storage
See here
eBay.co.uk: USB 2.0 to IDE HDD SATA ATA 2.5 3.5 HD Adapter Cable (item 170048986870 end time 17-Nov-06 20:13:00 GMT)
And no i dont have a vested intrest in this....you might find one cheaper elsewhere on ebay!!