Hi Ian,
Installing the SampleTank plugin *should* just be a matter of double-clicking on the file sampletank_2.5_setup.exe and clicking OK-Next-Next etc... Of course, you'll need to authorize it eventually, which is a few extra steps, but just installing the plugin for the first time, that should be it. [As someone pointed out there were some quirks during our beta test, but those were ironed out]
So apparently something is not happening as expected on your system, and we'd like to find out what it is - could you check a couple of things.... within Band-in-a-Box, open the VST/DXi Plugins window and let us know if you see it listed there, as in the screen shot below:
