I just finished downloading the first XIP/SYS from reeseboy (2302
- but since I haven't opened it yet I'm defintely not qualified to comment on how he packs them or what else he does. Maybe later. Otherwise you are correct in all your comments.
BTW - no offense was intended (downside to short posts sometimes) - it seemed to me reading your post that you expected something in the XIP to give you rounded edges. But reading again, you did say XIP/SYS so there was no need for me to post.
And to add detail to my post, the pretty edges come from .png files that are utilized by the gwe.dll as specified as part of the theme. The registry values for the theme are in HKCU\Software\Microsoft\Today. Your best bet is to find a theme that has the look you like and modify it. Classicblue.tsk comes with most of the WM6.5 SYS files and IIRC it has the rounded tabbed edges.