Mal said:
There are three types of points/SC upgrades.
I think you mean UC (Upgrade Credit) and not SC (Status Credit). note that after the end of this month (May 2007), no more upgrade credits will exist since they expire after 2 years and Qantas ceased issuing UCs on 25th May 2005 (also known as "Enhancement Day").
So after the end of May, the only way to pay for an upgrade is with QF FF points.
And to clarify, domestic upgrades (for flights QF400 and above) can be confirmed ahead of travel is there is U class seats available. U class is the availability bucket from which business class award seats are provided. If there is no U class available, then you can request an On-Departure Upgrade at the Qantas Club service desk from 2 hours before scheduled departure. You cannot waitlist for a domestic upgrade.
International upgrades can only requested through the waitlisting process, where the waitlist is evaluated the day before departure and services in order of FF status and the time the waitlist request was submitted.