i believe the High-Res is only available on the CDrom version ?
it's indeed started with the nascar -h command in dos / dosbox.
I got the trackpack too, but only on original disks, so without highres textures
edit: apparently the trackpack i found on the net says both versions have hres textures...i'm 100% sure my trackpack didn't have..
but anyway: there are 2 versions out there: one with original sponsors and Jeff Gordon on the main menu (i think its the nascar racing where "racing" is written in a yellow fancy font) and the one i got only has fictive cars, no real sponsors etc. (the racing is written in a white proper font)
got the trackpack disks but can't really install the tracks from the install.com -.-