Fairly often, I have friends who want a "road" bike they can use for commuting or recreational riding. And almost as often, those people eventual reveal the fact that they have an old mountain bike in their garage. For those who want to enter the world of riding-on-the-road, I just make one suggestion: Put slick tires on your mountain bike.
Yesterday morning I switched out these knobby tires on a friend's bike to some nice slick, cruiser tires. Her hot pink ride instantly went front slow and rumbly to quick and smooth. Higher tire pressure and smoother tread will help a great deal. And the gearing on a mountain bike isn't different enough for a new cyclist to make a difference. And to be honest, I would put most riders on a mountain bike for the riding geometry, comfort and steering control, anyway.
Don't think that you need those drop bars and tiny tires to ride on the road. Your solution may be hanging in your garage, waiting to be adapted. For the cost of slick tires, you can get a great road experience for very little investment. If you love it and want to go a bit faster, then you can start looking at those carbon fibre Lance Armstrong bikes :)