Colum, hope you don't mind if I rephrase that.
Adobe supports RH8 on Windows 7 32 bit.
That does not mean RH8 will not work on Windows 7 64 bit, just that it is not officially supported. It's the same with RoboHelp 7. It may work but it is not officially supported.
See www.grainge.org for RoboHelp and Authoring tips
I've been using RoboHelp 8 without issue on Windows 7 64 bit for a few months now.
For RoboHelp 7 I had to install the Microsoft Virtual Machine and run the Windows XP Mode. This provides a full working 32 bit Windows XP to use from inside Windows 7.
Helpful and Handy Links