Okay, I figured it out (guess that's what UltraISO help is for).
I extracted DVD boot image from the Win 7 DVD, then use ImgBurn to create the iso (I'm more familiar with ImgBurn). ImgBurn says it's creating a bootable iso image, we'll see soon.
I'll try it next with UltraISO to see if I can get the same results.
Found the ISO bootmaker by SIW2 which constructs ISO from extracted files: Boot to CD/DVD
Works great, takes minutes.
One step closer (perhaps)
Ran the cmd file, told it not to burn the iso now I can't find it. Looking at the cmd file, it should be called NEW.iso. Any idea where does it puts it? Looks like it should be in the same directory BootIsoMakerV2.cmd is in but it's not there.
I'll figure it out.
Edit: Found it. Wrote it to the root of the partition BootIsoMakerV2.cmd is in. Would be nice if the CMD file told you that. I'll fix it so it does the next time I run it.
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