Not wanting to be negative but... if you have to ask then I wonder if you have the business acumen and programming skills to pull it off. It's not just the crawling (that's easy, download http://www.phpdig.net/) but getting the algorithm right to prevent abuse by spammy sites and getting known by users. Don't underestimate the task!
What type of search engine do you want to make? One that will just crawl your site, or the Web at large? Or somewhere in between (such as just those sites you tell the engine to crawl)?
Here are a few links to PHP tutorials if you want to make your own... http://www.devarticles.com/c/a/MySQL/Developing-A-Site-Search-Engine-With-PHP-And-MySQL/ http://www.chauy.com/2005/11/create-a-php-search-engine/ http://www.phpriot.com/d/articles/php/search/zend-search-lucene/page2.html There are a lot of tutorials if you just search Google. -Jon