hello rasc sorry for taking so long to answer your question, I wasnt really here this weekend.
the ps3 has a couple of models out which mainly can be identified by there hard drive capacity. The first models where the 60gb and 20gb which both played ps2 games natively with a chip called emotion.
The second generation included a 40gb and an 80gb but the only one capable of playing ps2 games was the 80gb but this time emulating the ps2 games, most of the games run perfectly though but the ps3 got rid of the emotion chip that made ps2 games run natively due to cost in making the machine.
If you are stuck with a 40gb version your ps3 cant play ps2 games. Right now a new generation is out with an 80gb hard disk which is the same as the 40gb version but with more GB in there HD.
check the wikipedia for playstation3 and you will find a chart with the complete list of features of each model besides the ps2 backward compatibility they have even more stuff worth looking at.