If I were you I'd think about waiting for the next generation of Casio. I dunno how long that might be in the works, but I get very annoyed with the 1-button problem on my iPaq. As a simple example, think about just trying to run and jump at the same time in Mario...

You won't be disappointed by the power and versatility of the iPaq (I can't live without it!) but think twice if you only want one for games.

Or perhaps get a GBA, they're pretty cool... ;)