Yes, A rotozip will work.
It will be easier if you have all the attachments, inparticular the one that works like a compass (geometry, not nautical).
Drill the "seating" hole at the center of the point you want your cut-out to be, then use the guide to describe your circle as the rotozip cuts the material of your case.
Wear eye-protection as you will want to observe the cut as it is being made to make sure that it is clean and professional.
[SIZE=\"1\"]E6400 @ 3.4 , Noctua 120
7900GT @ 670/1680 , VF900
2 x 1GB Patriot 6400 @ 425
WD SATA 250GB
Neo HE 550
P180 / G15 / MX1000[/SIZE]