ok then, i take it you cant update the ghz then without getting a new mac?
And if i wanted to upgrade my memory from 160gb to 250gb how would i do this?
I read the 0.4GHz difference is minimum, you can't really tell, so don't worry.
As for the HD and RAM, they are both user upgradable without having to worry about the warranty, just keep the originals in case you have to sent the Macbook in for repair as Apple is not responsible for your new Memory and HD.
2GB of Memory is plenty for regular use and is still quite expensive, wait some more time,maybe and upgrade later to 4GB, for instance, it's supposed to be DDR3 1066MHz
as for the HD, as long as it's 2.5" I think you're good to go, Buy a case for the one inside your Mac and you can even upgrade to a 500GB and 7200rpm opposed to the 5400rpm you currently have.