The marked answer is valid, but not complete. There is another possiblity. This response is quoted from jktechnologies.com. The index crawl always starts at the root level site collection. If there isn't a root level site collection, the crawl will choke:
Your server name is “MYSERVER” and you have created a site
The site myportal isn’t on the root. When you browse to
http://myserver:84 you get a page cannot be displayed.
When you create a root site (Application Management / SharePoint Site Management / Create site collection) the search starts working again.
In my opinion it is a bit strange that this is needed but I am just a simple man….
This appears to have solved the problem and I am no longer experiencing the crawl problem. Seems like a ridiculous means of solving this problem, however this is using SP 2007... ugh.