I want to add some 120mm fan slots on my side panel case. The case is a Thermaltake Xaser which already comes with two 80mm fans on the inside the case itself behind the side panel held up by a plastic swivel device (check it out at NewEgg if you like), but I'd much rather have a couple of 120mms fans on the side sucking cool air in (plus I'd place the top 120mm fan over my heatsink fan to feed it cool air directly).
So, how would I go about measuring everything out? I do have a 120mm fan on my heatsink currently that I could use to trace everything, but don't you just trace the area of the fan and then mark where I need to drill... is it that simple?
Here's a pic of what I want to do: