I like it. Nice and clean. However the header is somewhat too big, you may wanna reduce the height a little. Good luck pal.
I also like the clean design... Not sure on first impression though what the topic is? Who are you targeting?
Forums are one of the toughest sites to get going in IMHO. No one wants to come if it isn't busy and you can't get busy unless people come and interact. Spending a few bucks for a logo or header wouldn't hurt you any. Some sort of semblance for your company can help make it look a bit more professional.