Depends on what version of the PS2 you have, if you have a Phat (old style version) PS2 console you can easily mod it by running some files through your MC and using ARMax cheats, which can be bought for 30-40 bucks at almost any game store. You also need a harddrive, Maxtor seems to work really well w/ the PS2.
Basically you can get any PS1 game and correspond it w/ your system to tell it there is a 'genuine' disc in there. Then there are certain files you can put on a memory card from using the ARMax to transfer it on there and it runs a launcher which allows you to run a program such as HDLoader or HDAdvance - I personally like HDLoader better. And then you can load your PS2 backups on your harddrive (IDE) and add/delete games by connecting it to your PC and doing game modifications on there.
Any questions I'm sure I and Teancum could help point you in the right direction for information.
Just thought I'd bump this topic - since I'd really like to see some characters be playable in MUA that T has done for XBox
Send me any files you have have for the PS2 T, it'd be appreciated.