^^ software emulation is possible, just because of the hardware of the PS2 and PS3, it is tough to emulate the PS2 on the PS3. PC's have a different architecture, so the way they overcame the difficulties of emulating a PS2 will not work on a PS3.
As for if they will ever manage it, who knows, but I am starting to believe that it will not be coming out at all.
EDIT: so currently, this is all fan driven rumors, based on that it is possible, and some guy at some store said 40GB will be packwards compatible.