From IPodWizard.net Wiki
Changing the graphics on your iPod is both easy and safe, so it is a good hack for the first time modder.
Before You Start...
NOTE: As of iTunes 7, you can only edit the ipod directly. iTunes 7 disables the previous updaters
How To Change a Graphic
- Load your iPods firmware
- Switch to the Pictures tab on iPodWizard. And make sure you're in "iPod" under "Edit Mode".
- Select the index number of the Graphic you would like to change, you should now see the image in the main pane below the index bar
for the purpose of this tutorial I will change the "Do not disconnect" image.
- After selecting the correct index number, click the "Load Bitmap" button. If you want to edit the original file, hit "Save Bitmap" on the right, and open the file in an external program. Alternatively you can click "Load All" to load a folder of images, which is useful for loading a pre-made theme.
- Now you will be able to browse through your files, when you find the image you want to replace the current image with, select it and click the "Open" button
You should now see the new image in place of the old one.
- Now click the "Write" button
A warning box should now appear saying "Are you sure you want to write the modified firmware to your iPod?" Click "Yes", now another box should appear saying "Successfully written the modded firmware to your iPod!" Click the OK button and you are finished.