Search engines categorize and search web sites based on keywords or concepts. Rarely do humans get involved. Automatic spiders crawl your web page and index it according to the words on the page, the page Title and meta tags. A search directory categorizes Web sites by subject and presents them according to relevancy based on what you enter in the search field. Most directories will not spider your site and some, like Yahoo, are manned by real people who have the final decision whether your site gets included in their directory or not.
Every search engine ranks pages their own way.
What works well on one engine may not work on another engine. To complicate matters even more, the search engines are constantly changing their search algorithms. AltaVista seems to change their ranking index every 6 to 8 weeks. If you are serious about using the search engines to promote and grow your online real estate business, you need to focus your efforts here. It is critical you use the geographic area you serve in your title as most people will type in a search that includes their geographic area of interest.