Sousuke has released the first playable game for PSP firmware V2.0, heres what he says:
1.) download the file (psp01.tif)
2.) put it in the PHOTO folder (you just need this one file - no background - nothing else).
3.) start it by pressing X on US PSPs (O on JP PSPs) on the PHOTO icon. Don't press Start or slideshow (It will just freeze and shutdown).
4.) if you want to shutdown, you have to hold the power switch for ~10 seconds (you don't have to take the battery out).