Party vs Party Campaign

[FlurryOfPosts]

I recently had an idea for a campaign involving two directly opposed parties. The campaign would take place in a world where arcane magic was banned by the church. One group would play arcane rebels, and the other would play divine inquisitors. The groups would alternate each session, with the arcane group going first. The goal would be for the inquisitors to track down and eliminate the rebels before they could complete some secret plan. If and when the inquisitors caught up to rebels, the session would end and the next session would have both groups fight PvP.
Have you ever tried a game like this?
What advice could you give to someone who would like to try?

[Quertus]

I was in a 2 party, "good vs evil" game.

Don't pre-script the ending - it may turn out differently than you expect. For instance, my party had the plan to a) find one or more of the McGuffin objects first, and replace it with a replica, so that the ritual would fail; b) use hit and run tactics to take out individual members of the other party, rather than engage them directly.

Don't play favorites. Talking to the other party afterward, they had done nothing to hide their tracks, yet nothing we did ever turned up any hint of them. Even though we had total logistic superiority, they were still constantly ahead of us. Etc etc. We had better strategy, better tactics, better builds, better builds synergy. They had DM favoritism.

Don't drag it out (but don't rush it, either). Especially if some people start getting picked off instead of dying in a dramatic showdown. Our game never came to a conclusion.

[daremetoidareyo]

How straightlaced can you play it?

http://www.blindpanic.com/humor/vecna.htm