I broke them up and was wounded. Warning, graphic, looks like slashed wrists: http://thespatula.livejournal.com/149521.html
We alternated which one got locked in the bathroom each night, until after a few months they didn't actively try to kill each other. Within 6 months or so they tolerated each other.
After thespatula moved out, and I moved into her old room, there were some new territory issues. Boo had claim to that room, while Charybdis had claim to whichever room I sleep in. Then I was away for a bit, and they kept each other company.
Now they nearly seem like friends: