Please forgive my ignorance on this one, but what is generally reckoned to be the best electric tool for cutting a window in the side of a case?.
I used a jigsaw on mine. Went through it like a hot knife through butter. Mask up the entire side panel (apart from the bit you are cutting). If your jigsaw has a metal base plate, put some masking tape on that as well (to stop scratches). Use decent quality metal cutting blades as well. That's about it really. Oh, wear eye protection, and cutting theroguh steel with a jigsaw is a rather noisey past time. If you have some ear defenders, wear them as well
I used a jigsaw with a metal blade (I got my blade from homebase - easy to get) and it cut with no problems. Take the above advice and don't cut corners with the masking - the base of the jigsaw badly scratches unprotected paint. It knackered mine.
I Dremeled mine, which was an exercise in patience, mostly. If you go the Dremel route, it's doable, but remember it will take several passes over your cut to break clear through the metal. Forcing the bit through or using too much pressure just wastes cutting wheels. It took me two reinforced cutting wheels and about 45 minutes to cut this: I'd probably second the jigsaw recommendation, though, unless you need a high level of detail. I just don't own one right now.
