Why do something so complicated when you can simply right-click on the folder containing the project, copy and paste to get a backup? (Windows will name the copy "Copy of Project" where Project is the name of the original folder; then you can easily rename it if you want to.)
Also, for people who aren't careful to put all their project files in the same folder, be aware that this will not backup files outside the project folder. So I strongly recommend making certain that all your files are in the same folder (you can check this by viewing the GDP file in notepad top see what other files it refers to. I believe version 1.x also has a utility included in the start menu that helps you determine the files related to a project).
(SGDK2 doesn't have this issue, BTW, because all content is stored in a single SGDK2 file.)