I was just browsing the Tutorial thread and this title caught my eye. Dunno if you've already come up with an answer or are still checkin' on this thread but hey, doesn't hurt to reply I guess. I'm no expert in WMM but I think I figured out how to do what you're looking for.
Let's say you import the two video clips and drag clip 1 onto the Timeline. Once it is there drag its audio track down to the Audio/Music track. Ya, this deletes the clip 1's video track from the Timeline but what can you do. That gives you a separate audio track for clip 1.
Then re-add clip 1 and mute it's audio track - right-click > Mute. Otherwise you'll have double audio tracks for clip 1. Now you've got clip 1's video and separate audio. You can trim clip 1's length as needed and then drag clip 2 onto the Timeline after clip 1. Mute clip 2's audio track. Now you have the audio from clip 1 playing the whole time, even when the Timeline passes into clip 2.
As for switching back to clip 1's video... You can drag clip 1 on to the Timeline again, after clip 2. Synchronizing the video with the Audio/Music track (originally from clip 1) can be a challange. You'll have to trim the front end of the second clip 1 video chunk so the end of it lines up with the end of the Audio/Music track. You can leave the audio track for the second clip 1 chunk un-muted so you can hear if the audio lines up. If they are off it'll sound echoy. Once they do line up, just mute the audio track for the second clip 1 chunk. Or basically, mute all the audio tracks aside from the Audio/Music track.
OK, so maybe that was uber-confusing... If it helps at all, hey, that would be cool.
P.S. Or, download the 30-day trial of
Sony Vegas 6 . I did and it was true love, lemme tell you! Now I'm working on some way of justifying its purchase...