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How to create .ISO from .VHD file - KezNews.com
You don't need a paid .iso editor, of course.
Extract the 7100 .iso ( which you are using as the host)
Replace the install.wim with the new one you just captured.
Use any pretty much any burning app. to create a bootable .iso from those files. If you have vlite, that will do it easily, or if you have the MS oscdimg.
Unless you want an .iso for some reason - you don't need it at all, it is perfectly easy to use the install.wim to install from.