Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Any S-ATA or P-ATA (IDE) HDD is capable of being put into an external Firewire enclosure, if that enclosure supports S-ATA or P-ATA.

Th enclosure you linked to is most likely using a cheap Firewire chipset and does only offer Firewire 400 (35 to 39 MB/S), but it really doesn't say. It's too cheap for a proper enclosure as far as my experience goes.

Have a look here (scroll down for enclosures): http://eshop.macsales.com/shop/firewire/on-the-go
 
I will second getting the OWC enclosure. I do not own one, but have seen a few and they look cool, and work great. And it will be a TRUE firewire 400/800 not a poorly made one like the one you linked to.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.