Autodesk has never said that they were going to update ACA '08 to natively
support a 64-bit OS.
In fact, they did say that they WOULD NOT EVER support it for ACA '08. So,
I don't know what you thought you were waiting on.
However, you can be pretty sure that '09 will be released by April (only 3
months away now, and the usual date for the Architecture product release
after the annual March release of regular Acad), and all indications are
that it will support a 64-bit OS.
Unless something changes before then.