monkeyman, I've removed the URL from the post as it is close to spamming - however feel free to add it to your profile if people are interested to check it out.
The best way to get members to join a forum is to get some good content on the main site - its taken 5 years for this site to get there so it does take time! Telling your friends about it is always a good way to build a few members, but beyond that you have to draw them in from the content on your site with interesting discussions
There is a very good forum which has a section on how to promote your site and optimise it for visitors :
www.sitepointforums.com. I've learnt lots from there over the years!