Try using the 3d terrain editor, draw an opauqe jelly fish profile any shape you want and then give it a guassian blur and smooth it and, also lower the height of it till it is the thicknes you want and if you dont like it you go back into the editor and mix a little more, I love the 3d terrain editor , once mastered it can create great results.

A good way to make natural looking smoke is to use the rock generator and filling them with a volumetric cloud or smoke fill, you can make them any size and shape and have no defining edges, just a thought, Awesome work.

Fireworks is a Macromedia prog, excellent vector graphics tool, the whole suite of macromedia progs are awsome.

What is the problem system crash, if so it is most likely your RAM is page faulting or just not enough L2 cache and a cluttered HD, and do you trim down your Virtual memory instead of letting windows use it dynamicaly.