I'd record your audio separately. It isn't that difficult and you could record to a cheap hard disk recorder, laptop or to a different camera. Matching up the 24p might be a little difficult unless you can specifically tell that recorder that you are recording in 24p. So, if you have a cheap MiniDV camera that can do 24p, record audio there. The issue is that the 5D and 7D do have a mini stereo input, but they have no audio controls, so the audio meter controls are always on. I suppose you could put a mixer in between, but it seems easier to me just to not have cables tied to your camera and record audio separately and slate your shots. Syncing them up is easy in Final Cut later.
It going back to our film roots in a way, but I don't consider that a bad thing. Just plan extra time to sync your dailies.
If you record to a laptop or disk recorder, there are some calculations out there that will allow you to slow your recordings down just enough to match the 24p, it is something crazy like 1/2 second slower over time, I don't remember exactly.
The 5D is the better camera, but the 7D has the rolling shutter issue improved, but I wouldn't be surprised if the new firmware update early 2010 fixes that as well.
I've shot on both and also on the Nikon D90 and i like all 3, but I've enjoyed the ease of getting a good image out of the 7D the most. Especially because I was doing some handheld stuff. But, if you are going to be on a tripod and not doing a bunch of giant fast moves, then the 5D is definitely the way to go. But, then again, it is also the most expensive.
-Tucker