While not a natural language search, I've used both Moodle's Glossary and Database activities for this kind of purpose in the past. For simplicity, I prefer the Glossary, though the power and flexibility of the database can be useful too.
Glossary has both search and browse listing feature, and entries can be tagged, though if you want an Ajax type search result that gets ranked you may be simply looking at ensuring your site has Global Search enabled, though I'm not sure if you could then restrict the results to only the support pages.
The Glossary entries themselves could have a summary of the help page with a link to the full page that already exists (or could simply be the link, or if you want to invest the time, the existing pages could be transferred into the Glossary itself, I'd recommend the summary and link to existing though)
Glossary has both search and browse listing feature, and entries can be tagged, though if you want an Ajax type search result that gets ranked you may be simply looking at ensuring your site has Global Search enabled, though I'm not sure if you could then restrict the results to only the support pages.
The Glossary entries themselves could have a summary of the help page with a link to the full page that already exists (or could simply be the link, or if you want to invest the time, the existing pages could be transferred into the Glossary itself, I'd recommend the summary and link to existing though)