Don't worry about it!
The first time I replaced a mobo in a system, quite frankly I was scared I was going to totally screw something up!
I had NEVER done this before & how was I going to remember where all those plugs and wires went!
But once I got in there it wasn't near as bad as I thought it would be!
You see everything has a "special" socket to where only one plug will fit into a socket a certain way! It's basically fool proof!
The only thing you have to do really is, Take Note of "how" the mobo is mounted!
Most will have Stand-Offs to keep the metal of the case away from the electronic contact points on the mobo.
Take these off the old mobo & put them on the new one.
(Depending on the mounting, they might be attached to the board, or the case. If the stand-offs are attached to the case just leave them where they are
as long as they line up with the holes on the new mobo, otherwise you might have to move them to an empty hole to line up properly.)
Tighten the stand-offs ONLY finger tight to the mobo as to not crack the mobo and break any internal traces.
(But not so loose that the screws turn around with the stand-offs like cloasters said)
The second thing will be the CPU mount. You will need to remove this off the old board and put that on the new one as well.
This is really easy...just put it on the new one the same way it came off the old one.
As long as you do this and take your time you'll be just fine.
And if your worried you will forget what goes where, then take a piece of masking tape and put a 1 on it and a 1 on the mobo where it plugs into on the new board.
I almost did this until I saw that the plugs and sockets were all fool proof.
