Trev dont worry ill bring you back to laymans terms now if you have a p4 now then if you get a X2 4200 it will be a HUGE improvement at the end of the day
You have to remember "pani k" that this chap is being confused by what were saying so i dont think he will be wanting to overclock a core 2 duo 1.8ghz to 3.0ghz or whatever by what i can gather he is just after a decent upgrade for not too much money, and the X2 4200 would be perfect for that.

Trev has enough info here(and with the links posted above) to make his own mind up what he goes for but ive given my 2 cents more than once