http://www.moddin.net/downloads.asp

Under "Site Stuff"

There are several templates there. Simple download one, print it out, and tape it to your case. Then using a drill, and appropriate sized bit, drill the holds. Then using a jigsaw or something similar, like a router or a dremmel tool, cut out the hole in the middle. Purchase some screen to cover the large hole and you're all set.

Should take a few hours if you are careful and cautious. Remember, it's "THINK-DO-THINK"

The screen should look like the link below:
http://www.moddedcomputers.com/mod/w...hole_grill.jpg