1. go to the root of your usb device or psp or whatever
2. make a new folder called ps3 (must be in block CAPITALS)
3. inside the ps3 folder you just made, make a new folder called theme (this must also be in block CAPITALS)
4. find and download a theme you like from the themes section
5. once you've downloaded a theme you like, right-click it and click copy
6. go to your theme folder in your usb device, right-click and click paste
7. when it is finished copying from your computer put your usb device into your ps3.
8. now on your ps3 go to theme settings and go to theme.
9. a list of options will come up. go to install
10. select your usb device and select the theme you want to install.
11. wait a while and it should install
12. go to theme settings and find your theme
13. press x and hit apply
There you go your theme is installed. get ready to show off your funky ps3 theme to your mates and let them get jealous.
If your still confused here are some screenshots to help you out.
METHODS OF INSTALL (Condensed Guide)
A) Download directly from the PS3 Web Browser
B) Download on your PC and place it on a flash card or USB device under the directory /PS3/THEME/
Note: The directory names must be ALL IN CAPS!
To install the theme take the .p3t file and put it on a memory stick in the following location: PS3->THEME->
Navigate to the theme setting on the XMB and you will have an option to install.
Choose install and browse to your memory stick.