Now if this were studio 8 it wold be easy to answer, you just click the little icon on the left the soundtrack on the timeline, to 'lock' it, then split the video clip above and delete all the visual you don't want and leave the sound behind. Then add the video clips you want, to the timeline, above the sound only bit, they will automatically drop their own sound.
However, when I installed Studio 9, which I bought as an upgrade without a manual, I couldn't lock either sound or video track, and as I also didn't get on with the compression to web size files, I dumped it and went back to Studio 8.
Another idea, again this would work with 8, if you drag a video clip onto one of the pure soundtrack lines, you just get the sound, so add your activities clips after whatever part of the pastor you want to keep, mute their soundtrack entirely, and drag the rest of the pastor clip onto one of the soundtrack lines under the activies. You may need to drag the whole clip then shorten it. You'd need to find a suitable pause in his speech to make it easier to cut.
Actually, thinking about it, you'd be better to put the rest of the pastor clip on the sound only track first, then add the activites to the video track, so you can trim the activities to match the sound, not the other way round.
Win XP, Athlon 1.8, G force 3 T, 1 60gig drive + 1 250 gig, Pinnacle Studio 9 plus mostly, Premiere 6, and Vegas 5 sometimes, Soundforge, Cool Edit.