This is a great tip for limiting the built in search functionality to search only the category you specify. The author provides the code for searching just a single category or searching only the children of a certain category.
This site is managed by Randa Clay who got tired of trying to keep track of all the cool solutions, ideas, scripts and bits of code that one day might be needed.
This is much better than searching around on Google and rummaging through my bookmarks for that thing I read a month ago. I hope you will find the site helpful as well.