your ibook has usb 2.0 and firewire 400, so it will work with 99% of external drives. there are some drives that also use firewire 800 (which is only on 15/17 powerbooks and powermacs) but they almost always have other choices. if the drive can use either usb or firewire, i think most people, myself included, would recommend you use firewire...
out of curiosity, what is the deal on this drive?
reality
edit: i checked memorex's website, and it seems they don't sell external drives... maybe you meant maxtor?
Personally, I bought a LaCie external drive because Apple seems to play nice with them. Occasionally you'll hear of some Apple update not being compatible with certain chipsets on a particular drive...but LaCie's don't seem to have this problem.