I figured I'd pass this on, because I never knew about it until about a month ago. There are a ton of premade files for Reaper on the Cockos wiki, including just about every Toontrack kit.
So go here, and download the files for the software you're using:
REAPER | Resources
Then in reaper, bring up piano roll, File (Windows) or Reaper (Mac) -> Load Note Names from File, and voila: