What kind of RAM can I buy to upgrade my new 2.0 MB?

Lenovo 2GB DDR3 SDRAM Memory Module - 43R1988 - Buy.com

Will this work? It says DDR3 but for a ThinkPad. Is there a difference?

May I recommend Crucial.com? Their pricing is very competitive, but it's still top tier memory, direct from the manufacturer with a lifetime warranty. If you use their memory advisor tool (on the main page), they guarantee compatibility.

Here is a list of DDR3 RAM. Any of these will work.

I have a new Macbook aluminium 2.4 ghz. Does it have 2 GB on 1 or 2 modules? In other words, do I need to buy a 4gb kit or just 2gb module? Thanks.