According to GamesIndustry.biz, Sony Computer Entertainment's UK studios are playing their part in getting PlayStation 2 backward compatibility up-and-running for the PlayStation 3 before it's (tentatively scheduled) November launch later this year. Backward compatibility on the PS3 will be achieved using software emulation, as opposed to the PS2's solution of utilizing PSX/PSone hardware built into the console. This is probably what you expected, considering the great differences between the PS2 and PS3 system architectures.
"PS3 Backward Compatibility On Track?" - 25.04.06