Microsoft announced on Thursday that the 64-bit version of Windows Vista will require all kernelmode code to be digitally signed.
This is very different than the current WHQL program, where the user ultimately decides how they want to handle unsigned drivers.
Vista driver developers must obtain a Publisher Identity Certificate (PIC) from Microsoft. Microsoft says they won't charge for it, but they require that you have a Class 3 Commercial Software Publisher Certificate from Verisign.
This certificate from Verisign costs $500 a year. More info over here.