Here I spent a few dollars on canned air. Of course it blows the dirt somewhere else! I wanted it out of my PC!
Watch the video at http://reviews.cnet.com/4520-11319_7-6240575-1.html
I have yet to clean the innards of my Pavilion desktop PC.
I had planned to use a vacuum cleaner, but was told that the effective computer vacuums cost a couple of hundred dollars. The battery-powered models are ineffective.He recommended a cannister of compressed gas instead.
The problem I have with the gas is that it is not removing dirt but blowing it somewhere else. On the other hand, it would be difficult to access all the 'nooks and crannies' of a CPU with a vacuum; would require a very small nozzle.
I would appreciate any recommendations you could provide.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic