I don't know about the memory card exploit - I use the PS2 HDLoader. Google it, I'm not sure if they still make it - I believe there was a legal liability regarding some code that Sony claimed was theirs.
But the PS2 HDLoader works great. The first time you run it and it sees that HD it prompts you to format it, and once that's complete you're ready to copy games to the hard drive. Thing is (and it shouldn't be a problem, since you'll be playing your games from the hd) that in order to access the hd, you have to boot from the HDLoader disc. I believe it was compatible with about 95% of the games. A worthwhile investment, and easier than a 26-wire solder PS2 modchip.
An even better investment would have a (modded) Xbox, since you gain much more functionality, but that's just my $.02.