That's quite a bit harder to do if you actually want to make it look halfway descent. Making it look ghetto style is simple. There is a new paint program out for XP from Microsoft but I can't remember what it's called, it's a beefed up version of MS Paint.
Or you could get crazy and attempt to learn Photoshop, that will let you do just about anything you want. Just ask Co-Pilot and DRTY!
