I'm guessing u know about sockets??, well i ll explain just incase u dont know, ok so think socket as in socket for ur power outlet, china and america has differnt sockets right.... so u can't use a american plug in china nor vice vercia(oh jst forget bout socket converters this is jst an example u cannot get socket converters for cpu's lol) so like Intel's cpu and AMD's cpu they each require different socket's, Intel's latets socket is LGA 775 and amd's latest socket is called AM2(or socket 940).
so u need a cpu that'll fit into a the right socket so u need a mobo and cpu with the same socket... but that doesn't solve all ur compatiableity(im a real bad speller) issues there, with different chipset(i guess the chips that make eveything talk 2gether.. on the mobo?? i think thats correct enouch) some may alow for anything(thats the same socket ofcorse and mostly newer or better/high end chipset motherboards) but older chipset's may not support newer processors even thou its the same socket. Usually when u read reviews or the specs of a Mobo, It'll tell u the socket type and what type of CPU's are compatiable.
At the moment Intel is leading the performance battle. I'd sagest a core 2 duo by intel socket 775, with mobo's maybe read a few reviews that's what i do before buying a mobo. I own a p5w dh deluxe its great i think its $205 at new egg. Read some reviews about it, the commando is also a good board as is the DS3 by gigabyte ... if ur getting a mobo i'd say stick with the big names , ASUS, GIGABYTE, ABIT and i guess EVGA(since they've made a pretty good name for themselves lately)
For processors u definatly want a duel core weather Intel or AMD from intel i'd deffinately recromend from the
E6xxx range or even x6xxx, and qx6xxx if u want to spend big bucks
from AMD you want
x2 4200+ or higher see what u can get for ur money the higher the numbers the better i think they go up 2 x2 6000+ (the x2 meaning duel core), if not in the x2 family maybe u want a FX something from fx 60 up is duelcore i think, there good for overclocking, and the optrons arn't half bad either as i've hear d but i donno 2 much bout optrons... well i think i've said enough for this post