you need a digitally signed driver in 64bit, either vista or win 7. But you only need the driver for overclocking, afaik everything else works fine anyway, if you need to overclock use a different tool.
Theres no real way around digitally signed drivers, you can(or used to be able to) do a single boot in debug mode, or some mode I forget the name of which will bypass the check for digitally signed drivers, but it won't load it on subsequant boots.
Anyway, from what I gathered the driver was only required for overclocking parts of the tray tools, I installed it yesterday, wouldnt' use the driver but had access to the basics that I wanted, since uninstalled though as well, I didn't like it much.