I was just doing a quick search to see if there were any good tutorials on opening/cleaning a computer and found this video. This guy actually disassembles the fan itself:
http://www.metacafe.com/watch/1695460/how_to_detail_strip_a_computer_fan/
Here are some good basic instructions for cleaning the case:
Case Cleaning:
This is where the dust goes at night to cuddle up with your processor. Dust is not your friend, it is not something to be laughed at, and it deserves respect. This is war ladies and gentlemen! Load up with some compressed air because you?re heading off to the frontlines! Actually, cleaning a computer case isn't that difficult. In fact, the entire process won't take more than about 20 or 25 minutes if the dust is really bad.
1. Turn off your computer.
2. Remove the side cover of the computer case, exposing the motherboard and other hardware components.
3. Inspect all cables and connections. Be sure to look for cables that are frayed, loose, pinched, snug or otherwise damaged. If you come across any cables that are damaged in any way or form you should immediately replace them. If a cable is frayed do not attempt to patch it up with electrical tape, this is very dangerous fix. We also advise that you replace snug cables with longer ones before it accidentally snaps.
4. Now its time to get out the compressed air. Shoot the canned air at everything in your computer. Pay special attention to the heatsink and fan on top of your processor. This area collects a lot of dust. Some other areas to focus on are add-on cards (audio/video/modem), case fans, hard disks, power supply and removable media drives (cd-rom). A vacuum may help suck out the dust while you knock it loose with the compressed air. Caution: Follow the directions on the back of compressed air! Do not spray hardware at close range! If you choose to use a vacuum, do not attempt to vacuum anything in your computer!!!
5. If you notice dust in the PCI and AGP slots of your motherboard it may be wise to remove each add-on card and shoot some compressed air into the slots to break away the dust.
6. If your case has an air filter remove it and run it through warm water to remove the dust. To dry it simply use a cloth (lint-free if possible) and gently dab away the excess water. Place the filter back into the case.
7. Replace the side cover of the computer, but check first that there aren?t any cables that are lying next to any fans. Fasten the cover and restore the power.
From here:
http://www.computerclub-brac.nl/schoon.htm