GuiKit2dlta can convert guikit to .dlta files:
http://mac.softpedia.com/get/Utilities/GuiKit2dlta.shtml
As of reading .dlta files in Windows, I'm still trying to figure out what dlta is...
Edit: I found this tool, hope it helps (if .dlta file's full name is In-Delta):
http://www.trapping.org/i-jpeg.html
@ Levi, I think it should be easier to create themes on Windows (specifically in SkinStudio) As all you have to do is import the pictures or the mssyle.
After reading some things about dlta, I have a feeling that you can open the dlta files to get the .tiff files inside. If so, can't you just import the .tiff to SkinStudio? (I think)
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