Thanks for the replies and suggestions. I've just had a quick look at the blurb for each one, so could be wrong, but all of those seem to require manually building an index of titles / keywords/ etc which the scripts reference.

The site I'm working with has 600+ articles. So I was hoping for something that would automatically generate its own index by scanning the text contained in all those articles automatically.

Perhaps it's not possible in a non-database site.