Well if you want to make a sig or something transparent, first, make it one layer. [skip this step if it is not a sig.] To do this, make a new layer and go to image>apply image. Then make all the stuff under it invisiable. [Ok, back on track] The pen tool is a great tool for cutting. All you have to do is place the anchors around the places you want to cut, complete the circuit, and then select it in the paths menu. Then erase that selection. You'll know it's transparent when you see the checkered grey and white. Then for everyone to see it in transparency, I just found .gif works with IE, and probably Firefox too. .Png's usually only work for FF.
Yeah. For transparencies just leave it on the checkered gray thing and save it as a .gif.