Did you know that Rockbox comes with a ready to use gameboy emulator called rockboy. Rockboy can play and .gb or .gbc game rom (.gba roms will not work).
1) Plug in your iPod.
2) Go to your ipod root folder.
3) Make a new folder and call it GBC.
4) Go on the internet and search for any gameboy or gameboy colour rom (ex. google search ".gbc rom").
 5) Once you find a rom that has a file extention .gb or .gbc only place it in the GBC folder you created.
6) Boot your iPod in Rockbox and click files.
7) Go into your GBC folder and click on the rom for the game you want to play.
8) To save your game flick the hold button while pressing the menu button.
9) A menu will apear giving you the option to save your game, load it or quit.
Enjoy your Game

1) Plug your iPod in and go to the .rockbox folder from within the iPod root folder
2) Make a new folder called doom.
3) Download this file rockdoom.wad
4) Place this file in the folder you just created
5) Enjoy your game