IMHO once a PC is over 18 months old its a waste of time & money to upgrade, beyond adding RAM, cards or extra drives. After, say 30 months its not worth doing anything. I think its much better to wait until you can afford a to build or buy a new PC. Preferably whilst your present PC works. My reasons are.
1. All the components are wearing out one way or another. The potential for grief is therefore higher than with a new machine.
2. Everything just about will have got faster & cheaper in the last x months.
3. You get plenty of time to test the new PC before using it.
4. You can network them as the easiest way of getting your data across.
5. You can then sell your old one as a whole, or in parts as you wish.
So a fresh start will be more economical in the long run. [blue]garebo[/blue] is right as far as he goes, so I guess I agree with him in the context of this thread. Also with [blue]danomac[/blue]. I'm certainly not trying to argue against them. I'm just saying that as the mobo/cpu/ram combination is so inter-dependant - changing one generally doesn't improve things much. You have to change all three at the same time. Video cards will have much more RAM & be faster so using the old one is again a false economy. You will probably crave a better CD/DVD combo & your hard drives will be wearing out, in addition they will slow your system down as newer ones will inevitably have faster data transfer rates, etc than your current ones. Other cards can probably be transferred. But again I would look to see what's new. Like If I was starting again I'd put in a 1G NIC card. - etc etc.
Reclaiming a PC for other people - like your kids say, now that's another matter entirely! But generally I'm afraid they get my old PC with the bits I transfer - well, missing!