Ok, I have recently seen the tutorial on the Swap-Switch method for playing back-ups, and on how you swap the disc's to trick the PS3. I have also been reading on the HDD Game Back-Up TIFF exploit using the HDD to freeze the PS3 etc..
Well i have recently found a new exploit. Unclip the HDD cover and unscrew that blue screw! DONT UN-PLUG THE HDD YET!!!
Go to Game on the XMB menu. Put in a Genuine PS2 game. Let the XMB load the PS2 disc, so you should now see the gold disc appear in the Game menu. Now scroll up too Game Data Utility and then go to the Network menu. Now switch back to the Game menu. You should now be on the Game menu with the Game Data Utility sub-menu high-lighted. Slide you HDD to the right using the metal leaver thingy your PS3's HDD should now be disconnected from the PS3. Now take out the Genuine PS2 disc and insert a legaly backed-up PS2 game, wait for it to read the disc. Now scroll down to the gold disc on the Game menu and now RE-INSERT the PS3 HDD by sliding it to the left, you might find the HDD a bit of a struggle to find the correct possition again but it should slid in eventualy. Once you have the HDD re-inserted press (X) on the PS2 game in the game menu. It should now boot-up. But will not load. I have only tested this on v2.01 so this exploit might work on lower versions.
This can also work with PS1 games and maby Blu-Ray
Post your findings