if you just want to replace gauges then the only program you need is notepad

don't change the gauge position and size values, just replace the name of the gauge you want replaced and it should appear right where the old one was
there is software like that you spoke of, but i find that the best way to know the coordinates for a gauge is by using photoshop or paintshop pro...
dragging a selection box around the desired area of the panel texture should give you the coordinates you need... then just copy them to the panel.cfg file
this reduces a lot the guesswork

Moach