Bicycling mag just had a great article in September on "Great Bikes for All Budgets"... you might want to check out the copy at your local library (if you don't subscribe ) check other back issues too, because they listed some good deals a few months ago (sub $600 for a decent road bike-- can't remember the brand)
you could also ask your LBS or any local bike clubs for postings about used road bikes... that's how i got mine.
but i'd definitely agree with the other posters here... ride it first!!! and then take it to a mechanic before you buy!!!
good luck, and happy riding