First of all, due to ESD (Electro Static Discharge) you must use caution when cleaning your PC. The most important thing (which I am sure that most of you already know this), is NOT to use a household vacuum when trying to clean out your PC. This is basically guaranteeing that you will get ESD degration (no immediate harm, but computer will slowly get worse and worse).
There are computer shop vacuums that guarntee no static electricity. These vacuums can be found at any computer store, but they definitely lack the sucking power (those on the consumer market are way too weak to do any good). Those that are made for professionals (with large sucking power), are too expensive to even bother buying.
As stated in the previous posts, I suggest the compressed air. However, you must have a foot of distance between the PC and the spray, and you must NOT have it spray the same area for more than two seconds. If the spray is too close or is on for too long, a layer of moisture will cover the surface. This moisture may cause harm to video cards, motherboards, sound cards, etc. You can buy compress air from many computer retail stores for only ten bucks.
About your problem with your fans, if you are a big computer gamer, an easy way to improve performance is to try to leave as much breathing room for your video card's fan as you can. You can do this by moving components into a different PCI slot that is further away from the video card. This has happened alot with those who have bought HP or Compaq computers recently. The 56k card is literally suffocating video card fans, causing them to run that much hotter. In most cases, people have removed this card (since most people only need to use their ethernet connection) altogether and had XP autoconfigure the connection.