You should read the entire license, but the gist of it is that you can do anything you want with the code, including sell your new version. The catch is that if you distribute new binary versions, you are required to make the entire source code available for free to everyone. This is why Quake has been ported to other platforms such as Linux and Mac. Another datapoint to remember is that Quake used to run at 30 frames per second on my old Pentium 200 MMX . On an overclocked iPaq this translates to a predicted 25fps Quake performance on the iPaq.
Some people strongly prefer gamepad.
Some people strongly prefer stylus. I prefer stylus, and also my hand doesn't block screen. Therefore, use an arrangement similiar to the following. These instructions should work well either in normal 240x320 or sideways 320x240 mode when holding the handheld sideways. Recorder button is JimmySoft's standard menu button as you may notice in Turjah.