Recently I've been investigating the effects of changing the relevancy of MOSS search.  If you are interested in this, you might want to check this out:

Evaluating and Customizing Search Relevance in SharePoint Server 2007

After you through reading the article, you can download a cool tool to help you test your relevancy adjustments Search Relevancy Tool.

Changing the weights associated with managed properties can be found at How to: Change the Weight Setting for a Managed Property.

If you have success with your adjustments, drop me a note.

<additions when="Nov 1, 2007">

Enterprise Search Relevance Architecture Overview

Improving Relevance

Also, check our codeplex, it also has some cool stuff.

</additions>

</steve>