You shouldn't need to dust 'cept when upgrading.
Just think about the placement of your computer, and of all the inhaust fans.
Is there a carpet in your computer room? BAD
Is your computer resting on the carpet? WORSE
Is your carpet pink and fluffy, carebear style? ....[*i]
If you find your computer becoming dusty often, get some neat fan mesh filter
which you can remove and clean every once in a while, and apply to all fans that are
sucking the air into your computer.