Hmmm....to run your home brew stuff....Snes emulator for example
For non Hard drive added PS2's (slims inc) I think you need USB Advance to run/read the connected USB drive - for more info:
http://www.hdadvance.com/Not sure where to purchase it from now...site links above mainly are dead
Of course to add a HDD to a fat PS2 you need a network adapter and an IDE HDD - but to run from the HDD I used to use HD Advance to run my hard drive equipped PS2 but now use McFreeBoot (over to Mr Phu for more on that one) which runs of a modified Memory Card.
