For a forum, how about PHPBB? It's free and easy to install and configure. http://www.phpbb.com

Someone else will have to advise you on your other question.

I use a PHPBB forum. The installation was pretty smooth and I was was able to modify the theme but I was getting spambot posts everyday.

I had to change the visual confirmnation (captcha) over to a textual confirmation that asked a question that must be answered correctly, and haven't had a spambot post since.

I would recommend you use http://www.simplemachines.org/ as it it too has a nice installation script and the theme can be modified easily. I haven't had any spambot posts on this forum.

A php script would do your zip code search