hmm, i wish i still had a copy of cs3 i'd be able to figure it out.
my best guess, is that, when you have artboard 2 selected, and you go to save for web, you need to make sure that you click the check box (on the right, towards the bottom, second tab) that says "clip to artboard"
let me know if that helps, i'm pretty sure it can be done though.
-matt