lets take riceball for example, he has a nice cpu but a crappy GPU, thats why he cant play all today's games. so he shuld have put that money to a 6600GT or 6800 and then he wouldnt be kicking himself and his emachine
well it really depends. you need to do some research on the specs of your mobo,it will tell you the processors it will support, so i would suggest going to their website and checking that out. if you dont know what mobo you have, download everest home edition to find out.