Old iPhone + computer switch = syncing troubles

Hi everyone,

I have an iPhone 4 running iOS 4.2.1 - it was last synced a long time ago. Back then I was syncing it to my iMac.

Since then, I have downloaded all sorts of apps on my phone and no longer use the iMac in question. Now I am using a Macbook Pro (currently running 10.6.8, but tonight I'm upgrading it to Mountain Lion).

I want to sync my iPhone (and update it to iOS 6) with my Macbook Pro, keeping all the apps and app data from my phone but replacing everything else (music, etc) with what's on my laptop.

How would I go about doing this?

Thanks!