You can use Adobe Photoshop like TimFlem pointed out. Or you can try using Paint Shop Pro. It's not as good as Photoshop but it's good enough to make decent looking signatures and avatars or whatever you plan on doing.
<div class="quote_poster">Quoting KS1:</div><div class="quote_post">How much did you buy the photoshop for?</div> I didn't buy it. Got it from a friend
Photoshop is about 600 to 700$... so here's a little advice, download it on kazaa its 164mb and after everybodi's happy, except Adobe, but who cares
95% of the walls on www.walls-cave.com and www.wcremix.com are made with an illegal version of photoshop, so feel free to use it