It sounds like this is your first use of (VST) plug-ins in a DAW. Is that right?
When you install the MP2 software you get a load of files installed into (on Windows) a sub-folder in the C:\Program Files\IK Multimedia folder. These files include the standalone executable program (a .exe file) and another file that is the main software functionality (a .pak file)
The MP2 installer also installs the plug-ins. VST3 and AAX plug-in files are normally installed into sub-folders within specific fixed folders. The VST plug-in can go almost where you want. These plug-ins also use that .pak file that I mentioned above.
You can tun the standalone MP2 program directly or you can run a DAW (you mentioned Reaper) and load the plug-in onto a track in the DAW. Just as an example, here is SampleTank 4 VST2 plug-in in Reaper:
So, the plug-ins are not integrated and can be used in a DAW, but they do rely on other files.
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As for location, my IKM plug-ins are in a folder named C:\VST_64 Plugins\IK Multimedia and the VST path in Reaper's Preference Settings is C:\VST_64 Plugins.
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As for the sounds library:
-- what problem did you have with IKPM?
-- what executable did you find and where?
-- what is the full path name leading to the MP2 instrument files?
-- what is the full path name leading to the MP2 samples files?
-- what path is selected in MP2's Preference Settings?