Site integration

Hi,

I would like to build my website around the Web Wiz Forums database, so if a user registers on the forum, an item in the site menu shows they are logged in on all pages, including non-forum pages. How can I go about doing this?

If a user visits one of my own pages and they have logged in before, how do I auto-login that user?
And how do you check if they are just visiting and need to register? Are there cookies to check or something?

Thanks.