you dont have to do that group box edge in magic pink anymore, nowdays windows7 and vista accept png for that.
i wouldnt bother skinning the header, leave it as it is, 1 pixel image in magic pink.
the header never seems to look right in alot of places, from my own experience.
you may look at my template for it if you wish its callled "group_box" in my fearomone skin
just so you get an idea....