Go to your local K-mart or Wal-mart and buy cans of conpresses air.. that'll blast that dust right out of everywhere.. Also.. To prevent dust from getting inside.. Use Alluminum Mesh filters.. Put them in front of your fans.. I'll sell you some if you want.
Just rember... Unplug the machine before opening it.. Everthing should be safe to clean.. Buyt i would use a can of air for the most safety
I actually just did that today. I don't have compressed air cans, but what I used was an air compresser (can be found at most auto shops) and just stuck a small nozzle on it and blew all the dust out. Also, one tip I will add is that if you run a fan on your video card (most geforce4's have em, along with newer radeon's) pull your video card out and blow the junk off that thing. Dust in a fan can sometimes gum up the bearings, causing a slower fan and less cool air on your GPU.
Actually, thats not reccomended. A little bit of moisture can screw up the internals of a computer, and your breath is very moist. Really, the all around best way to go about it is to use compressed air....
Also if your going to take off the cover to clean dont touch anything unless you ground yourself first like put your hand on the metel of the side panel.Static electricity can fry you parts.Just a tip.Also a cotten swab to wipe off some of the buildup that wont blow off easy.Later Pat S