Uhmmm... yes, you can by pressing F8 at boot time and choosing to ignore the warnings about unsigned drivers, but you have to do it each and every time you boot. There is a way to permanently disable that driver signing requirement but I'm leery to give out the info anymore since it hosed a few people's machines recently.
It wasn't my fault that they chose to continue using shitty old drivers, but they blamed me for the mistake they made anyway.
Vista x64 is a more secure and stable OS than the 32 bit version, and that's one of the primary reasons why: the driver signing requirement. Disabling it or 'getting around it' will more than likely end up causing you issues at some point.
Google can find the specific method to disable the signing requirement permanently, or a search here might find it since it's been posted about 3 times over the past 4 months or so.