I'm too lazy to dig up the link to the message where I posted the details, but the easy way to put a blowhole into a case is this:
Mark the locations of the four fan mounting holes. Center-punch them (to keep your drill bit from wandering). Drill the four mounting holes. Using a straight edge, draw an "X" connecting the diagonal pairs of holes. Center punch the intersection. Using an appropriately sized
hole saw, drill through. Clean up the sharp edges of the hole with a round file or a rotary tool with a grinding cone attachment. Attach fan and wire grill using regular self-tapping fan mounting screws. You can mount the fan grill from inside or outide the case for a couple of different looks. The inside mounting option leaves the screw heads flush with the outside of the case and the fan grill just slightly protruding through the hole.
I put a nice 92mm side fan on my Antec SX1030B. Of course, I did spend $15 on a hole saw specifically of that size.