the first tow version of the consol (the 20 and 60) had EE (Emotion Engine) hence full hardware support for PS2 titles. then the 40 and 80 replaced theme, the 80 had sofware emulation (wich works just fine for moste ps3 titles, first hand tried ookami FF12 Metal gear 2/3) the 40 one never had and never will support ps2 games. and since this august all support for ps2 titles on any consol has been removed.
so unless the consol is made to execute unsigned code (cracked in other ugly words) there's no way in hell to do it.
ref wikipedia page on PS3.