To add my experience to qhawk's solution (I cant just add a comment directly under the solution as I have less than 50 rep) - in SharePoint Designer 2010, I had to go to Site Objects --> All Files --> then select the relevant Library which has the page you want to copy, copy it to another Library, e.g. Shared Documents, rename it there, copy it back, job done.
I found that if I just selected Site Objects --> Lists and Libraries --> and chose my Library from there, it wouldnt list the actual items in the library to be able to copy them, not even in the Views or Forms box. You have to go through the 'All Files' route.
PS. I know this is an old thread, but I found this whilst trying to find the solution for this, and after finding qhawk's solution needed a little tweaking for me, thought I'd let others know incase someone else stumbles across this.