Creating index from HTML keywords in HTMLhelp workshop

I realise that it's not spcifically a VC++ issue, but can someone please tell me how to automatically create an index from keywords in html. I'm using MS help workshop 1.4 (a terrible product, with ironically the worst help in the world).
In the project options, on the File tab, I have checked the Include Keywords from HTML under the index section. I'm putting <meta name="keyword" content="blah"> tags into the html files, but after compiling the help, the index is empty.

I would be very grateful for any ideas.
Thanks
Jon