Okay, blackcurtain, I think I may have figured it out, but I'm not sure.
I thought I had already done this at least once, but on a hunch I saved the image as a 32-bit .tga (I think they had all been png's before that) and it seems to have lost the jaggies for me. Very strange, but it looks to be a flaw in the conversion from png to tga within Skinstudio.
I'm going to do a little more testing later, and I'll get back to you.
-Asp
I think maybe your right. the orginal image I posted above was only a temp to show how bad I was getting pixealted. I tried several variations of similar shapes and kept getting it. so I decided that since it is my first skin and learning PS at the same time I would simplify it an just go with the original default shape of a flat top with rounded corners. this helped but I was still getting very pixelated on my rounded corners. was trying anything I could think of, reading tutorials on rounded corners with glaussan blur, alpha channels etc...
in the end I remade the rounded corner image 3 or 4 times, each end result had varying degrees of pixelation though the image size and rounded corner size was the same, suddenly with one remake I had no pixelation. (maybe it was that degree and contour thing that vStyler mentioned, I thought I had kept them the same but with so many remakes who knows, maybe I just got lucky and chose the right combo of angles,contours and highlighting.)
So I too concluded that it was a result of or combination of (in no certain order)
a: my system not rendering transparency well
b: SKS not converting .png to .tga well and losing some of the transparency (though I had the same problem when trying to save the image as .tga rather than .png
c: my very basic knowledge of PS and not knowing what to do to fix the problem.
Funny though the StartMenu Top part is the only image I have had the problem with so far. thus until I learn houw to fully utilize the incredible power of PS, I may find myself remaking images to solve transparency problems 
