Can you please post some pics up of both cars/panels. This will help get better answers and ideas.
I have recently cut that panel out of (unfortunately) a rubbish car. Basically you get a grinder and cut on the out side of all seams and body lines that join that panel to the body, plus the inner wheel arch, rear bin, etc etc.
Also where are you located? another member may have a doner panel or a car worse off that the one you are planing on cutting up, also you may be able to repair the current car instead of replacing the entire panel.