It looks like it's finally out, well not exactly VAST but something quite similar, even better. It's called Memor32 and with the unofficial Memento firmware, it seems like you can boot anything without voiding your warranty.

The best part is that you can plug an usb HD on the ps2 and it'll run games stored on it. Too bad the ps2 only has 1.1 usb ports.

I played guitar hero 2 for a year with my slimline ps2, I think it's about time I unlock it to play these games I had before my phat ps2 died.