You mean in the description of the site in the search engine rankings, right? Specifically MSN, as the only search engine I could find any of your pages indexed in.
Well, you can't explicitly control what is shown by any search engine, although there are various ways you can try and nudge them in the correct direction. Unfortunately, designating specific parts of a page as non-indexable is not one of those. Mind you, doing that to your menu would be a bad idea anyway as you definately want spiders to index your navigation.
You might consider some or all of the following :
1. Write better meta descriptions, which can be picked up if relevant to the content on the site.
2. Move your menu to the bottom of the source code, and position it via CSS. This will mean search engines will hit your written content first.
Actually I thought I'd have more than that to offer you but to be honest this is not something I've ever come across before. Weird.
If you're really desperate to put across the right image in the SERPS, make the navigation graphic based. However, from an SEO perspective this comes highly unrecommended.