I'm in the same situation. I wanted to start riding in club rides and long distances; but all I had was my heavy steel non-suspension mountain bike. While the majority of road bikes will be fine commuters, some aren't designed to be. My Giant TCR2 doesn't have mounting points for rear racks or panniers - its built to run. Once I got the giant I tried to use it to commute, but I got scared locking up my nice new bike outside my office. So I converted my mountain bike into a commuter - slick tires instead of knobs, a rear rack, panniers, clippless peddles. Its well over 40lbs loaded with stuff for work, no speed demon. But with a 30 mile commute each day, when I get on my giant on the weekends I FLY. In short, keep the mountain bike commuter; it'll handle the potholes and the load fine, and it'll train you to drop everyone and buy a starter road bike - don't go with Giant at Performance (they stopped their contract so service will be difficult). Check out the under $750 road bike thread in the Road Cycling forum, there are some great suggestions there if you can find an LBS that carries the brands.