As a team-building exercise, my company has got us making movies. I've somehow managed to volunteer myself for the editing role.

This means that I've got to take a bunch of footage (which we're still in the process of filming) and edit it down to about 3 minutes.

First: what tips do people have for this kind of thing?
Second: what software should I use? Windows Movie Maker doesn't have enough features.

I need to take the original video, overlay voiceover, and cut back and forth between at least 2 video tracks.

I've tried Pinnacle Studio, but it's a bit flaky (I thought I'd lost 3 hours progress this morning), which doesn't inspire confidence. I also tried Magix Movie Edit Pro, but the performance doesn't appear that great, in that it can't preview AVCHD in real-time (it appears to use 2 cores to do the rendering, but I've got 4 cores, so it's missing a trick there).