Question regarding backup

So I had a quick question about my 3.1.3 backup. Excuse me if this has been answered elsewhere, but I haven't been able to find any thing regarding it so I figured I'd ask.

About a week ago I updated my iPhone 3GS to iOS 4 GMC on a buddy's mac. Before hand I had made a back up of my 3.1.3 firmware on my windows computer. I've been waiting for a public release of iTunes 9.2 to sync my items on my computer. But I had a question about my 3.1.3 back up. Can I restore my backup data to my phone while keeping the iOS4 GMC?

For example, if I restore using my backup will my old texts and notes still be there?