I probably have as many questions as answers:
Search by category: Where is the category information? You might want to look at the Taxonomy feature and tagging. If you are using something like Ventrian's News article module, I believe that there are some search my category features, but nothing site-wide.
Advanced Search: The DotNetNuke search module will search for multiple words. For more, you will need a different module, I think.
Relevance: The DotNetNuke search module does compute a relevance number.
We have a tutorial: How to Setup and Configure the DotNetNuke Core Search
This may help in understanding search:
http://www.dotnetnuke.com/Resources...earch.aspx There are several advanced search modules available on Snowcovered. Also take a look at
http://www.dotnetnuke.com/Resources...dule.aspx.