re: circular saw. Because there are a LOT of different types of saw. Hand saw, rip saw, jig saw, router (not computer router), bandsaws, reciprocating saws (the almighty Sawzall!), etc.
I highly recommend building your next PC in an old filing cabinet, like a 2 drawer one.
You can easily fabricate some wood blocks/spacers etc for the fans and stuff, and just drill out the vent holes for the exhaust. You can put all your operating CDs and junk in the bottom.