The article on LN working with REAPER for MAC is good but for us Windows/Linux guys, a similar article using Windows at least will be very useful.
Liquid Notes works with Reaper also on Windows.
On Windows machines, the installation package of Liquid Notes comes with a third party MIDI cable/driver called 'LoopBe 30'. This is a virtual MIDI cable that establishes the connection between the DAW and Liquid Notes.
Same as in the article for Mac OS X (see: http://re-compose.desk.com/customer/portal/articles/1418504), you route the different MIDI channels between Reaper and Liquid Notes - caution is on numbering the channels, so that you don't cross-connect something wrongly.
We'll add a video and article to the FAQs shortly, and update this thread!
All the best,