This great new mod which will be included in future version of phpLD adds an advanced search to your directory, allowing for a more customized search of links, categories and articles. You can choose to sort the results by Relevancy, Title, Hits or Category, and can limit your search to certain categories.
To download the mod, visit the thread in the forums
Advanced Search for phpLD
Demo: Advanced Search on Directhoo
Here is a screenshot of the Advanced Search in the default template: