Hi lakeshore...
The NI-CAN 2.3 driver software does not support the Windows NT 4.0 operating system anymore. It's not that the installer simply doesn't let you install it, but the files that are special to that OS are no longer in that package.
The latest NI-CAN version that supports Windows NT 4.0 is 2.2.1. You can find that download
here.
-B2k