The first step is always to measure. Here's a picture of my case with shiny yellow tape on it to mark some of the lines. Using a pencil I carefully measured out all the dimensions of the case window. The corners of the window will be rounded out so that I can install molding around the edges. In this case, we hadn't purchased the molding yet so we are just going to cut out the window. There are all sorts of things that can go wrong when you measure incorrectly (as we shall see). Because the case is a low-profile micro-ATX case, I had to be extra carful. This case is about the size of a 15" monitor and about 2.5 times as deep. The case fan is 1" deep so I had to be careful that it wouldn't hit again any of the PCI cards or the processor fan! All in all it was a tight fit. I ended up with a 12" by 12" sheet of plexiglass. for the window and blowhole.

Another Case picture - (click to enlarge)

Next: Using the Dremel