How do I duplicate my xcode project? (iPhone SDK)
By the way, I simply duplicated/renamed the entire project folder. But when I started working in the new (duplicated) project (after changing app ids, provisioning profiles) I started getting errors about targets. I have no clue about what targets are or anything either so. Hmmm. Hope this works.
An alternative - consider getting a free source control system like svn, git or mercurial (or perforce or other commercial systems offer free licenses for limited use)* and then do anything you like to your project. You can always go back to an earlier version if you don't like the results. If you want to get more complicated you can branch it. This is one of the biggest steps you can take towards working in a professional manner.
*anything but Visual SourceSafe. Don't use that! CVS is probably best avoided too.