I read a great article in Aurthur Frommer's Budget Travel magazine sometime in the past two years a feature on the very topic of barge travel. Now, the article focused on doing this in France, but it may give you some leads on where to find resources on the web for barge travel.
www.frommers.com.
Obviously, you can get good connections to Europe via UA/LH out of either SFO or PDX. PDX-FRA-FCO would be a likely routing for example, but LH flies to just about everywhere in Europe.
Also check out fodors.com.