I tried this already. In fact I set it to just index the ubb folder and ran re-index. PHP is in the list but I suspect it is not indexing the files with ###.inc.php Still no success most of the time.
Mine is able to find strings in *.inc.php files. I didn't set anything up special to have it do that, so I don't know what to tell you. I'm using Vista Home Professional SP1. (Came with the new laptop)