I'd be happy to help if I can. I guess it must be down to some seemingly insignificant difference that's causing the installation to fail, sometimes. A couple of possibilities on my end may be the fact my win7 installation disc is Dell branded, and may have some other differences, other than simply branding the OS with the Dell logo, etc.
One other thing. As my MAME PC has no internet connection, I downloaded the CRT emudriver + tools package on another PC. Then I unzipped it, copied the files to a portable drive, and copied them onto my MAME PC. I've just remembered that this sometimes changes the files' attributes to read only. Maybe this has an effect?