The thing is, it's made with syslinux and has VistaPE on it which is Virus INFESTED! (the image I used was, apparently, NOT clean).
a clean (no non-related to the question files) directory dump of the root of the drive:
boot DRIVERS Standalone WinApps casper VISTAPE.CFG VISTAPE.WIM WIN51 WIN51IP WIN51IP.SP3 Launcher.xml Launcher.exe BOOTMGR autorun.inf
The question is: what would be the proper way to remove VistaPE from it by replacing it with a bootable live Windows7 install?
I suppose I can clean the vistape from it. Then build the live 7 on a different USB and just put it on my old one, modifying the boot record config files (syslinux)?