i was looking in to this nearly a year ago, but it's only for the full size PS2 as bill says, not the slimline one that i got for christmas last year.

there was talk of a usb version then, and it looks like it did happen, called the USBeXtreme. having a quick read, it looks as though you need to back up the games onto a your pc's hard drive running win 2k or xp, and then connect to the slimline PS2 (or normal one) usb port. but loading times are no better than loading off original game dvd. you still have the advantage of 'backing up' all of your games to one place and not swapping discs, as well as perhaps less legal uses.