Well, looking at the ads on the pages (the forums link seems the same as the main link), they don't look very related to the content at all. This could be part of the fault of why your CTR is very low, accoring to the typical 3.0%.
Even though you are not currently with Google or Yahoo, you might want to think about switching. Google Adsense along with Yahoo Publisher Network are the most popular PPC ad programs out there that can customize to your site just as it is now.
As for ad optimization, check out
Google Adsense Suport - Ad Optimization, its a great resource, and can be applied to most ad service providers.
From looking at the colors you are using, you are definitely blending the ads in with the content, which is always a plus. I think this is more of an optimization deal which deals with:
1) Getting a more keyword-centric ad provider.
2) Looking at where the prime areas of a site are to place advertisements.
What kind of traffic are you getting to get that 0.5% CTR. It could also be a bad sample.
Anyways, let me know if you need anything else, I would be glad to assist you.
-Steve