Do you ever plan on signing the 64-bit winpkfilter drivers available for download on the website? The reason I ask is that Vista 64 will not load unsigned drivers unless you specifically tell it to on a boot-by-boot basis.
Taking into account that WinpkFilter is a development library but not an end user software we don’t find its drivers signing really necessary. When it is used for evaluation or private/non-commercial purposes it can be loaded on Vista x64 by choosing the “Enforce unsigned drivers loading” option in the boot menu. In case of commercial usage WinpkFilter custom build should be signed by the end vendor by its own signature.
Our current point of view may change once Vista x64 becomes more popular when it is now.