Most PlayStation 3s are not backwards compatible, but Sony may be investigating an external adapter to act as a bridge. Japanese message boards are buzzing about a patent filed by Sony Computer Entertainment Japan for a new generation to previous generation console adapter. We checked the Japanese Patent database to verify and a patent indeed exists.
A schematic of the proposed adapter (200) shows the device has its own processor, a DVD decoder/emulator, sound processor, and graphic processor.
This is a patent application so no guarantees, but if a PS2 to PS3 adapter came to market would you buy it?
Update: Here’s the patent, saved as a PDF.