How to prevent a computer from becoming dusty?

The most important thing to do is to have some good filters on every fan that blows into the computer. In addition it can be very smart to have more fans that sucks in than blows out. This results in air going out of all the potentially unfiltered holes instead of in. Having a computer elevated a few inches, doesn't really help much. My brother had that, and his computer was full of dust when I checked it recently.

I have had this setup for years and the computer is pretty much dust free inside. Just remember to take out the filters and clean them once in a while for example by carefully vacuuming all the dust off of them. Should maybe be done 4 times a year. Maybe more, maybe less, all depending how much dust you have around :)

Personally I bought some filters that were specially made for 120mm fans (which I had), but I think that a friend of mine actually cut some pieces of a pair of nylon pantyhoses and I've been told it worked quite well. Haven't tried that myself though... so don't really have a clue :p

Keep the computers off the ground. Keep the room clean. Clean the computers, at least blowing the dust out, every six months. It's probably not worth going to more effort than this, since dust doesn't really do significant harm and periodic maintenance is a good idea for reasons other than dust.

On top of the fans/filters, one of the more interesting ideas I've heard is to put silica gel packets (like those often shipped with athletic shoes) in areas that you don't mind dust (the bottom, away from the boards).

The idea is that you can decrease the overall humidity in the case, so the dust sticks less to the components, and more to the packets. That makes it a lot easier to clean.

You put a filter on the intake fan and about every six months you drag it outside and blow it clean anyway. Works perfectly. I have my computer on the floor and make no effort to keep dust away from it. Try not to use a vacuum cleaner if you can avoid it, since it causes static electricity to build up and can potentially destroy components, use a can of compressed air or a compressor instead.

As Rowland mentions, you should of course clean or replace the filter now and then, check it every month. There are special computer cases that are constructed with this in mind, such as the P182 from Antec.

Basic steps to mitigate dust:

• Keep the computer as far away as practical from carpets and soft furnishings
• Clean the area around the computer frequently

Whilst you can get filters, don't forget to replace them, because otherwise you may adversely affect the cooling capacity of your system, and end up toasting the unit.