Jacques, I havn't seen 1.5 for a while, so I need to stress that what I'm about to say is more of an educated guess linked to a rough memory.
Each audio track in the mixer has a small chip (tickbox in 1.5??) that you click in order to enable that track for recording. In CS3 it's a little microphone.
Having said that, I DON'T think that's going to give you what you want, as the intention of the recording functionality in PP is to record audio FROM AN EXTERNAL SOURCE (like a microphone) straight to an audio track, say, when doing a Voice Over for some video.
You can't "mix down" to the master, as the master is not a track per se. It's just a "final" level control. The master will always be the sum of the active tracks, and THAT'S what will be rendered in the final output.
You can still "live mix" your audio with the faders, it's just that those movements get recorded as keyframes on each of the tracks you modify (including, BTW, the Master).
The advantage to this workflow is that every fader move you make is infinitley editable... a small error when riding the faders can easily be fixed by dragging keyframes.
Thanks for your reply. I see your point now. Somehow the fact that the Master track (and every other Submix track) does show up on the Timeline along with other Audio tracks led me to the impression that they were in fact output tracks that could be written to by the Audio Mixer.
Thanks for correcting my understanding.
Glad to help.
The master is on the timeline with the others so that you can keyframe "level" by CTRL clicking (I guess!)