'Blarney,

One more opinion supporting NOT swapping rims, just use the mountain bike rims with a tire with more of a "road-type" lug* pattern. This way you only need to swap tires (and not rims; $$)when going from road to mountain biking. This works really well and gives you the "Jack-at-all-Trades" thing you mentioned. If you are at all tentative about how this is done or what to buy, talk to your Local Bike Shop.

Ciao, bello!

* - Technical term for "treads", those bumpy things on mountain bike tires that grab rocky, muddy, and uneven surfaces off-road.