For anyone interested:
Two great suggestions on how to paint rain were made to a recent post I had placed
here. It occurred to me that it would be beneficial to share with everyone to
maximixe the benefit.
a) A Goggle search on Michael Kutsche "concept to character" reveals a free download and full workshop involving rain. (PDF).
b) Issue 16 of Digital Artist has a six-page tutorial with nature artist Amber Hill on how to paint rain in Corel Painter X.
Credits and thank you's to John Malcolm and April Madden for their timely and knowledgable suggestions.