Your 4 lines only center the panels. The code that eleroux came up with resizes and repositions every panel no matter where it's at on the screen(so theoretically no matter what resolution you are in, each panel will be the same size and in the same position). However, if you're using a single, large panel with buttons then the center only solution should work if you design all of your panels that way.

Scaling down an image should lead to a good result, but Photoshop is probably using special filters whereas 3DGS probably doesn't(maybe it does...I haven't inspected the manual for newer panel features/flags). If it scaling down doesn't look good, then the only other alternative is to create a set of panels for each supported resolution and swap out art on the fly. You can still use the code, above, though(albeit modified) for positioning).