I'm thinking of developing a recently acquired domain and I am looking for something to install that will let my users login to the forum, photo gallery, and a classifieds section and I want to be able to have 1 login for all of them.

Is there any open source software to do this, and/or 2 or 3 different products that I can easily integrate?

Also considering using VBbulletin because I know it can intgrate with photopost which also has classifieds but I have to pay for 3 licenses and I havnt heard anything good about photopost. I also am considering developing a network of these somewhat social networking sites and thats when the licenses will start to get expensive.

I appreciate any advice.

Thanks