here and here have relatively good how to's. just remember, to line up the mounting holes for the motherboard right (some pc's have raised mounting holes and some have screw in hexagonal pegs, that are usually copper colored, just line them up as best you can with the mounting holes on your mother board). Screw the board in firmly, and don't use screws that are too large or go over the little grounded area otherwise it could short (and it would be a damn big screw too ;) He're prolly want you're going to want to do in order:
1.) Disassemble case as best as possible (depending on how it comes apart, you'll have to get to the left and right sides of the case to remove some screws)
2.) remove old pci/agp/isa cards
3.) Remove all cables from board as best possible.
4.) remove old hdd's and optical drives (have screws on both sides of the case usually) & cables
5.) remove old cpu/ram
6.) Unscrew old motherboard, remove
7.) Remove old powersupply
Now the thing should be pretty much hollowed out. Usually for me thats the easiest way of dissassembling a pc, and putting it back together i usually do the opposite order.
Now before you get all gung-ho and put the new mobo in, replace the io shield in the back with the one i linked to on ebay if the refurb doesn't come with one (which it prolly won't, since i bought an a7n8x-dx refurb and a7n8x refurb and neither came with it, all that comes in the box is the motherboard and perhaps a manual) Which leads me to my next point, if it doens't come with a manual, goto asus.com and print the pdf for it because once your comp is apart, with no manual it can be trick to get the pc to work again.)
Anyway, once you line up your mobo with the mounting holes (which basically equates to you holding the mobo over the emptied out case and eye-ing up what holes are the closest for your boards, being that not all boards use all holes and if you have a mounting post in the case thats not for a hole, it may touch an electronically sensitive part of the board cosing a short.
Over all its not too tough. once the board is mounted. Once thing about the heat sink/fan. When you are puting the thermal compound on the cpu, only put it on the little metalic rectangle (aka the core) in the middle of the chip. A dab about the size of a small piece of rice should do, no more than that tho. Put your finger inside a plastic sandwich baggy and smear the rice sized piece around the top of the core to spread it evenly. The baggy will retain some of the cmpd, but as long as a THIN layer is spread on the core its ok.
Next, up is the Heatsink fan itself. You'll notice on one side, above the 3 holes they normally have, there is an outward notch (this is usally closer to the side on the bottom of the heatsink that is indented to fit around the upper part of the cpu socket). What you want to do is line up the side with the 3 holes that do not have a notch first and then on the opposite side that does have a notch, use a small flat head screw driver to apply a good bit of pressure to clamp down the other side (it sounds rather complex, but if you do it once in your life you should be good forever. Its kinda hard to explain, but you'll have to be careful here, you have to push pretty hard to get it down, but not too hard so your screw driver flies of and knicks something important on the board).
After that its smooth sailing. The RAM Dimms can only be inserted one direction due to notches on the bottom. The power supply should be able to be slipped in and screwed back into place. PCI/AGP cards should fit right in and now since everything is mostly assembled you can put your hdd and optical drives back in. The final part (besides plugging in the eide cables, perhaps the analog audio cable if you still use it, plugging in the fans and the psu, is plugging in the LED's on the front of the case and the power switch. This is what you NEED the manual for. The board may have some markings as to what goes where, but trust me the manual makes things much easier to make sure you hook up the HDD LED to the right place, the reset switch, the power switch, the pc speaker and what ever else your case comes equiped with (per haps a sleep button or a keyboard lock, etc... not much stuff has it now adays but some cases do.) Other than that, you should be able to fire it back up and Win98 will crash and shit all over you due to all the changes. So be prepared to reinstlal the os :-D
_ _ - - = = Pr3tty F1y = = - - _ _