"Stephane Letz at GRAME, of JackOSX and jackdmp (multi-processor jackd) fame, has been working on a Windows port of JACK (specifically, jackdmp), and reports early initial success. We apparently need a new ASIO backend, and there is much other work to be done, but the basics appear to work satisfactorily. The original author of JACK is preparing to eat hats, crow and his own left foot as payment for all the times he said it could not be done. Watch this space for more information as it happens."
And by that time, Vista may be a reality, and may include this functionality--hey, who knows?