How does stationary biking (like the ones you can find at any gym) compare to road biking?

A little background: I live in Newfoundland, Canada and 8 months out of the year it is ALWAYS too cold to go out. The other 4 months are pretty volatile too, but you do get a few nice days. It's kind of like playing Russian Roulette.

Because of the situation with the weather and the fact that I'm in college, I can't justify dropping any money on a new bike right now. As it is we're in the last weeks of the "warm months" and starting in September I'll be back in school and I'll have access to the stationary bikes in the university gym for free.

Eventually I do plan on getting a bike (if even just for use in the summer months), so what sort of differences can I expect to notice when I go from a stationary bike to a road bike?