I've done the drive bay fan window. It 's small its simple and it ain't enough.
I ordered a square window kit from Maplins,
the cheapest place I could find on the internet at £9.99 + p&p. It
came within a couple of days by 2nd class mail.
You can see the specifications in the picture. It came with a nicely cut rounded
piece of perspex which had a layer of papery type stuff on it for protection.
Also in the box were: a set of instructions, a load of rubber moulding, a rubber
locking strip and a small washer.
The instructions weren't particularly helpful beyond explaining the inclusion
of the washer; although everything else was self-explanatory.
The first thing I did was remove the side panel of my case and coccoon it in
masking tape - I didn't want to scratch it the way I had so many other cases.
I then chose where I wanted the window and placed the perspex on the side panel,
making sure it was parallel to the edges.
This is where the washer came in. You put the washer next to the perspex on
the side panel. Then get your pencil and place it inside the washer and run
it all the way round the edge of the perspex. This give you the exact width
required for the rubber moulding. The line left is where you cut your hole in
the side panel.