First things first:
Installing RockBox will void your warranty. Also I am not responsible for any damage and/or data loss done installing RockBox on your iPod.
Proceed at your own risk.
Ok now thats over with heres what you need.
it can be a nano 1st gen, ipod 1g,2g,3g,4g or 5g but not classic.
(if you dont have a clue which iPod you own have a look at this. http://support.apple.com/kb/HT1353)
-The .rockbox build. get the appropriate one for your iPod here: http://www.rockbox.org/download/
- ipodpatcher: this handy little program will patch the bootloader on your iPod so that it can load rockbox properly. get it here : http://download.rockbox.org/bootloader/ipod/ipodpatcher/win32/ipodpatcher.exe
EXTRA: To enhance RockBox you can get extra fonts get them here
To run the game plugin "Doom" you'll need a base WAD
get it here : http://download.rockbox.org/useful/rockdoom.zip
That's it. Your all set.
Make sure to view the pictures and screenshots in high res
Step 1: Extracting
If you haven't got one yet get the right one for your iPod here: http://www.rockbox.org/download/
(Make sure you get the right one. Don't get the 30gb video and 60/80gb videos builds mixed up)
Extract the '.rockbox' folder from the zip to the root directory of you iPod's drive. (the root directory is the main directory of your disk. e.g E:)
If your iPod isn't showing up in my computer, it is because you haven't enabled disk use
You can do that by following these steps: http://support.apple.com/kb/HT1478
Now we can move on to the next step.