Eyyyyyy, Vielmond! I use Photoshop CS3. If you go to file>save for web and devices> and then set the preset (below the save, cancel, and done buttons) to PNG-24 and check transparency, you can get rid of the non-transparent pixels in your work. This way if you've drawn something that you just want to show up on a web page with no frame, you can do that. I think a mask will make your background square again, though. I'm not sure.
Thank you for taking the time to show me how to mask things properly! I had a more round-about way of doing that, yours is more direct.