i have 2 qusetions
One:can you control your psp with your ps3
and
Two:how come the 60 and 80 gb PS3 can play ps2 games and the 40 gb ps3 can only ps1 games

2: because the 40GB one was stripped of most important component that made the PS3 backwards compatible, namely the PS2's Emotion Engine.

One: No.

Two: PS2 games on a PS3 use hardware supported emulation. The 40gb SKU lacks the PS2 hardware needed in order to cut costs.

Don't forget that the 60gig version is not made anymore and it can play mostly all the ps2 games and the 80gig version plays more than half of the ps2 games.

Remember that is only the case for the US and Japan. PAL units play less than half the games properly, regardless of which unit you have.