Although I have a 1.5 firmware, I once upgraded to 2.0 and downgraded back to 1.5, so I have experience with the TIFF loader. Here�s what you need to do

1. Read on how to connect you PSP to the computer up above.
2. Download the loader by Fanjita, [Only Registered users can see links . Click Here To Register...] for you guys
3. Unpack and transfer the files under the directions of the Readme.
4. Load your homebrew the same way like the 1.5 instructions.
5. Go to your PSP and go to the Pictures option, select the eBoot loader.
6. Instead of loading a picture, the crack is activated and you get a list of the available homebrew.
7. Select a homebrew and enjoy

There is more detailed instructions on the Readme, including how to use the WiFi option. I recommend you to read that first and follow it more.