Yeah it's becoming a little clearer.
Found this site that has some useful info about PureVideo and PureVideo HD:
http://www.nzone.com/object/nzone_pvhd_build.html
Also this comparison of features between ATI's Avivo and Nvidia's PureVideo:
http://tomshardware.co.uk/2007/01/09...-uk/index.html
So it looks like if you've got a compatible geforce card you can have PureVideo/PureVideo HD without having to purchase the codec as it's in the latest versions of forceware.
If you don't have a geforce card you can still use PureVideo via the codec available either supplied with some players or from the link supplied by Valley.
To make use of PureVideo HD (which is for Blu-Ray or HD-DVD) you need some of the new player software with HD support built-in from PowerDVD, WinDVD or other popular alternatives, as and when they become available. As far as I know either PowerDVD 6.5 HD or PowerDVD 7 Ultra will do, no idea about the others.