Custom Database Search – Can it be done?

I’m looking for some help or direction for a project I need to have done.

Im using wpmu as a cms tool. I need to create a custom search box on the homepage that will search certain categories for keywords over the blog network to pull in relevant posts to that search criteria.

(Keyword + zip code + 30 mile radius)example

I would also need to add a advanced search page if someone gets to many search results.

My blog authors will be writing posts, but they wont ad the right tags all the time or some may not even bother.

I know there is the plug-in called search everything, but I’m not sure if that this is the answer to my problem.

Id like to know if this can be done, and how to go about it. Id thought I would start here before asking around on the other forums and elance.com and guru.com