mnoGoSearch on Windows?

According to the PHP manual, the mnoGoSearch extension is not available on the Windows platform. I had considered installing mnoGoSearch on our Windows box running PHP (even though I will have to pay for the Windows version of mnoGoSearch). However, now that I've seen this in the manual, I want to know what my other search engine options may be (for preferably free, open-source software). The search engine must index the site like a regular spider, and it should include have the ability to include PDF docs, Word docs, etc. and be configurable enough to exclude certain folders, etc. I would also like the ability to access the engine through PHP, if possible. Any suggestions or favorites out there? I would prefer not to write one on my own. Thanks. -Ben