An anonymous developer has released a PSX (or PSOne) emulator for the PS3 — you can call it PS3SX. Consider it a pre-release that runs at full speed, full screen and features 2-player support. Currently PS3SX is a hybrid using bits from the leaked [official Sony] PS3 SDK and the open sourced PSL1GHT. The source code will be made available once it can be compiled under PSL1GHT alone.
You will also need to obtain the PSX BIOS (SCPH1001.bin) by some other means, like Google for example. We won’t be hosting the BIOS here. Find that, download it and the PS3SX archive, follow the instructions and enjoy some crusty-looking PSX titles on your big screen!
PS3SX Pre-Release Features:
2 players
All ISO formats
PSX homebrew *.psx and *.exe
Save works for player 1 & 2
Sound support CDDA and XA
Full screen
Full speed