Yeah, it's not really two separate sites I'm talking about, more of a subsidiary site, I was more looking at branding two different parts of a site to feel like a different website and accessed via different domains but in reality it was the same site (sharing forums). Not sure if I will do this but wanted to make sure that using two different domains on the one install was legal. Obviously in the future, if I needed two separate sites I would of course buy a second licence as it's definitely worth it.
I understand all the above but I wondered about this scenario: Say you have a website called www.all_about_apples.com and you use IP.Content as the front end and IP.Board as the community. You also have a smaller website called www.all_about_oranges.com using something like wordpress or joomla. Can you decide to integrate the two, but retain their independence. What I mean by that is, could you link the domain name www.all_about_oranges.com to an IP.Content page(s) on the "apples" site and from there link to a dedicated forum within the apples forums. i.e. both sites use the same install but their front end pages are styled differently and they share the forums system. Basically, can you legally run two or more sites if you only use the one install?