1. Download and install ISO Master via Synaptic Package Manager (search for "isomaster" without the quotes.)
2. Launch ISO Master from Sound & Video in the Main Menu.
3. Tools > Options > replace "mousepad" with "gedit" (again, without quotes)
4. File > Open > select desired ISO image (in this example, we'll use the Windows XP ISO mentioned above)
5. Let's edit SETUPP.INI: In the bottom pane, double click the I386 folder, right click SETUPP.INI, and click Edit
   
6. gedit will open SETUPP.INI. Make desired changes.
7. In gedit, click File > Save > and then close gedit
8. In ISO Master, click File > Save As > type a new filename (it will not allow you to overwrite the original ISO image) and click Save.

/nix | Jun 19, 2009