I have an old laptop that I don't really use anymore, but I think would be useful as a desktop. Are there any instructions for taking a laptop motherboard and putting it into a case and converting to a desktop?
Don't bother taking it apart - just imagine the existing laptop case is your desktop's new slim case.
1) Since you sound like you're comfortable opening it, if you do, clean the fans and cooling tubes/fins with a light bristled, non-static brush. If you don't see the fans and/or heat sink, skip this.
2) The advice about the laptop cooling device is good but can be overkill (and add to noise) if your existing fans are running fine. Especially if you can clean them out.
3) Most laptop already have a VGA out - some recent ones also had DVI out. Since yours is old, it'll probably be VGA. Note that the VGA resolution may not be the latest and greatest (i.e. it could be less than 1080p). Plug your existing monitor's VGA cable into that VGA out display.
4) Reuse your existing AC power adapter
5) Buy/reuse a keyboard, mouse
6) Power on and enjoy !!
I have my laptop on a desk open, I never use its mouse or keyboard, but it is plugged in to a KVM and I use a external keyboard, mouse and monitor (Can't imagine many people who are on this site who do not have these spare lying around!), I got an USB to 2x PS2 ports off of eBay for £3 (including shipping).
I keep my laptop open because I use dual screen feature.
(I am just kicking myself as to why I spent so much on this laptop, when I should of just got a desktop, I hardly ever take it around with me!)