Just use the psx game exploit to install the hdloader software on your memory card
It's even cheaper than buying the hdloader disc. I've got it installed on my mem card, I just need to get a network adapter and I'll be good to go.
I've got a few questions for those of you with the hdloaders though. Can you copy your game save files over to the hard drive? Also, is the file system the same as a pc uses? For example, can I keep moving the hdd back and forth between the computer and the ps2? I have some back ups of games stored on one of my hard drives now and I'm wondering if I'll be able to copy them over to the hard drive I want to use for the ps2.