One of the most annoying things about the PlayStation 3 is its lack of backward compatibility on some models. There are several hacks out there to do this, but most of them involve extra hardware, like the Cobra-USB Dongle, or downgrading, which can cause all sorts of problems.
Photo by borisvolodnikov
But in just a few minutes, you can install this PS2 software emulator to make your PS3 backward compatible. You can download the file here, but before you get started, you may want to make a backup copy of your /dev_flash folder since you'll be replacing some files. As with all hacks, you run the risk of doing damage to your console or wiping it clean if you're not careful or are unsure of what you're doing, so proceed with caution.
Here are the original instructions posted on PS3 Dev Wiki:
1. Replace following files on your consoles /dev_flash/
with the ones included in this archive
2. Get into Factory Service Mode (FSM Tool/Dongle)
3. Insert your Original PS2 Game Disc
4. It will run.
If you don't know how to get into Factory Service Mode, this page should help.
Have you tried any hacks to make your PS3 backward compatible? Let us know how they've worked for you in the comments.