Try different advertisements on your forum, not just leaderboards but also other sizes. You could also try InfoLinks for advertisements on keywords, that might bring in another bit of revenue.
For a forum topic, you might place a square at the left of the content, so that the text is at the right next to the ads.
(Have you even considered changing from theme, many people are used to see this template as default and can easily filter out the ads )
On your homepage your ads aren't blended in nicely. You might also try the 248*60 ad right above the posts.
On a SEO point of view, have you thought about changing your permalinks? Might get you better SERPs