I'm in agreement with Corsair - I suggest a hybrid.

It's a good way to get started and even if you decide to make the jump to a roadbike in a year or two, you'll have a good bike to toodle around town or do some commuting with. This is what I did. I bought a Trek Hybrid (7200FX) - they run somewhere around $350. There are lots of other brands, too. It was a great way for me to get started and test out my knees and committment to cycling before I plunked down $1500 on a roadbike. 8 months later - I bought a roadbike. But I do still use the hybrid to run errands and take the kids to the park, ride with my daughter, etc. I have a friend that's been riding a hybrid for years and goes many many miles!

Good luck and let us know what you decide! Feel free to ask more questions - that's why we're here!