Named Iphone 3g Back up's

In my back up list I have 2 old Iphone back ups (not sure how they got there) and a current one which backs up every time I sync.

I want to create an additional back up and name it ie iPhone back up 21-11-08, so I can back on certain date, keep this back up and stop it from being overwritten when auto syncing.

Any idea how i can do this.