Just a quick tip for anyone looking to have their Windows hardware WHQL’d (e.g., given a “Certified for Windows Vista” logo, etc.) – Microsoft has made 64-bit drivers MANDATORY. If you’ve designed a hardware product and you want to get it certified, you must also submit an x64 driver. The following text is from the Windows Logo Program Device Requirements Document (pages 86 and 365 as of today – search for “x64”):

All products and drivers (kernel mode or user mode) submitted for Microsoft signature or Logo must support the x64 version of that specific Windows operating system, with certain exceptions described below. This requirement is applicable for Windows Vista and later operating systems. It applies to all logo‘ed and unclassified drivers. x86 driver submissions are optional in all cases. When submitting an x86 driver or device, vendors must also make an x64 bit driver submission.

Just a warning before you get far along the process to get your product tested for WHQL/DTM.

However, Microsoft has been giving a 60 day grace period in which you can submit your x64 bit drivers.