Hello,
first impression, the welcome box, you need to customize this,, what you have is completely stock.. tell ppl why they should sign up and visit your site

also, this is a great place to add your keywords and key phrases..
This style is nice, I like it.. but it needs updated to 3.6
You have a good number of forums,, now to keep adding content and post..
you need to work on SEO..
removed, "powered by vb"
add your forum descriptions on show thread. and do
this edit on postbit
I can see a few more things, but this is a start for you.
good luck and pm me if you want some more suggestions