I just bought an authentic Dremel. It was meant as a gift for Els until I noticed I could cut away parts from my computer cases with ease, and maybe give that old computer a flashing new look, air brush it to make it look good.
Words are easy to say, the only possible next step is to get in action and do a test job. I took an old mini tower, made a I/O design to go in the side, and put some cool colors on it to make it look a lot better. Along with myself, Murphy's law came in action and everything that could go wrong, needed to be learned. Here are some tips if you're planning to do something alike, and maybe you don't want to go through the hassles of the problems I encountered. It is really satisfactory to work on your own cool case, maybe in your own "shop," so I'd like to encourage everybody to start working on one on his own. So here are my ideas on how it should have been done, if I try it again.
Your Dremel is your friend. But use it with safety and patience. Wear protective glasses when cutting and let the speed and right bits of your Dremel do the works. The reinforced cutting wheels are excellent for cutting through metal, your regular set of manual files are good for removing irregurlarities, and the green stony bits are just perfect to round your cutting edges and to finish off corners. The steel brushes are great when removing paint from metal, before sanding it off with the highest grit sanding paper until your fingers don't feel the bumps. Again, all the bits are perfect if used with patience. If you're cutting lines or other shapes, work against the direction of the rotation of your bit. This makes it less jumpier as it can't grip itself in already cut material.
Use masking tape to draw your design of cut outs on the metal parts of your design. It also protects your case when cutting. If possible, work on the invisible parts of your metal to make your cuts to prevent more damage. I had the bad luck of having to work with a U shaped metal sheet, and I reinforced the shape with some boxes so I could work on a steady piece.
Put your work piece on a table cloth or something else to protect the other side at all times. Iron particles and the likes will scratch your metal, and it will be hard to sand paper and air brush them away.
Don't just assume that any kind of air brush paint can just sit on top of another layer of paint. Always use a neutral primer between layers, and test out the results on a test piece before applying it on your metal parts. I had the bad luck of mixing two layers of paint, having to sand everything down again as the whole upper layer started bubbling...