When i link to the main domain does all my forum sepr raise or when i link to a certain forum does the sepr raise? which one is better linking all my link gamehaxerz.com or gamehaxerz.com/forums/
It truly depends on what you want the focus of your site to be. If you want primarily a forum community, especially if you have products that can be sold through the forum, always link to your forum. So many people know about DigitalPoint forums that have never actually gone to digitalpoint.com Now, if your forum is merely a sideshow of your main site, there's no real need to promote it outside of your site itself unless you're looking for a larger userbase. In this case, link to your keyword rich domain and within your site make call to action buttons to register for the forum (and make it simple registration! people hate filling out lengthy forms)
yes it depends on for what you need traffic. Choose appropriate one which would be useful traffic for you.