I installed symbola months ago but nothing uses it. Do I have to edit the registry entries related to font fallbacks? What have I failed to do?

The old one didn't have these symbols. When I installed it on debian linux (called: ttf-ancient-fonts - but you have to use the testing repository) it was used immediately.

Well I remember testing it on love hotel, which I specifically checked was in symbola if I set the font manually. But it wouldn't render if it was embedded in normal text.

It's probably been more than five years since I've installed a font under Windows, so I'll just hope MSFT's own tutorial answers your question:

http://www.microsoft.com/typography/truetypeinstall.mspx

The main site for symbola is here: http://users.teilar.gr/~g1951d/

That site seemed to be down when I posted.