I would say yes you need an editing program. Most icons are not jpeg or bitmap format. A lot use the png format that allows a clear or erased background. It is still square but it appears to be round as that is all that can be seen.
Droid I- Rom, crap which one did I load again?
As already suggested and tried, GIMP is great. If you just want to make a few icons though, you could also get a trial of Adobe Creative Suite which includes Fireworks and Photoshop. I find that casual users like Fireworks better where as they find GIMP and Photoshop a little difficult.
Just throwing it out there for others.