@ gurus um... AFAIK, Mac processors are
not a user-accessible part. the proc upgrade is done in the factory, IINM. I'd recommend wah chai to get ACPP...
@ wah chai i'll apologise for being direct, but your method of asking is a bit unhelpful. its like walking into a shoe store and asking "what shoe is good?"
it depends on what you want. if you use your Mac for websurfing, iLife and MS Office, 4GB RAM is more than enough.
if you plan to do movie editing etc, get the i7 so that you can do more editing and processing in a shorter time.
if you can't afford possible repairs / failures of your Mac, then
definitely get AppleCare ...
but if you just come in and say "I got no money, but I don't know what to buy" ... no one can help you