You may want to take a look at
http://www.interactivetools.com/products/realtymanager/
It's not free, but may actually be worth it in the long run for a real estate type website, unless you've got the time and knowledge to code up something yourself.
I don't know how you can get all of the real estate listings in a certain area. I'm sure there is most likely a database of all the listings kept for your local area somewhere though, possibly even online somewhere. You may want to just try a few searches for real estate listings in your area and you'll probably find something. You may also want to look at
http://realtor.com/Default.asp?poe=realtor