The big thing that hurts machines is blasting all that dust through the power supply, making the fan sing a high E, burning out the bearings on the power supply fan, and causing that huge gout of dust out the case vents. Why is my description so descriptive? 'Cause like a dummy, I used to do that...

Keep things grounded to drain off any static charge. Pull the power supply. Block the fan so it doesn't spin. Use lower pressure air. Try to avoid blowing dust from one assembly across another.

Don't put a tower section on the floor under the desk. That's where all the dust your feet stir up gets sucked into the power suppy. You think it's nasty when a cat brings up a big ol' hairball? You've never seen a double Pentium motherboard pukin' up dust bunnies the size of baseballs...

The air filter idea isn't bad. Just clean 'em regularly, and make sure they don't restrict aif flow to start with.

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"If a tree is cut down in the rainforest, and is used to make paper to print a book, and the book is really bad, and there's nobody that will read it, do you still hear a sucking sound?"
Charlie in Dayton, A.AsC.