Last week I had to crawl a site with case-sensitive URLs. After some troubleshooting I found out that this feature is *not* enabled by default in MSS. I found this great post by Richard on the Enterprise Search blog:

http://blogs.msdn.com/enterprisesearch/archive/2008/01/25/crawling-case-sensitive-web-content-in-sharepoint-server-2007-and-search-server-2008.aspx