Limiting Adsense to certain text

I use Adsense as a way to try and make a little extra cash off my site: I’m not trying to make it a real business or anything like that, I just figure that I may as well do that. I haven’t seen a cheque from Google yet, but it’s only a fairly low traffic site (2-300 hits per day, and most of them on a few posts, including one Sudoku post I wrote ages ago. Still gets more comments than all other posts combined too…). Anyway, Adsense seems to think my site is all about blogging, when it’s really not. I have written several blogging related posts recently, but there is more depth to my site than that. Occasionally I get AppleScript Ads, and sometimes some Psychic Ads (!?). What I think is happening is that many of the posts are short, and Google indexes all of the page, but it looks like most of the page is about blogging, due to the text and links in the Sidebar. I’d like to be able to tell Google that the text that the Google Ad should be about is the stuff inside the <div id="content"> -- </div> tags. Then, Ads would actually reflect what I’m posting about. Instead of always being Ads for the same few blogging companies (especially Square Space…).