Get the GCN version. Online play on the PS2 is capped at 8-players and 99% of the user created maps are horrible. GCN version is a little smoother with sharper textures. Great game by the way, it's a shame that it recieved such poor sales. I think it is time Free Radical started a new, but similar, series.
Now that I think of it, I'm not 100% sure, but I think that it has roughly 4 controller setups, so I don't think you can customize button layouts.