How do I set up the screensaver/wallpaper when I have just updated my Iphone 3g to 4.0?

I have just updated my Iphone 3g to 4.0 software but all I have different is the folders for the apps. I know some of the new products dont work on the 3g but being able to have a background where your apps are should. I am unable to access this. If I goto the pictures and select one for my wallpaper thats all I can do. Please Help
Many Thanks in advance.

that is not available on the 3g.. sorry my kid has it and all you really get is the folders