First, I have to say that I meant "newlines" rather than "linefeeds." I guess I was having flashbacks to my days working on mainframes (despite that comment, I'm in my early thirties). Next, I'll be looking for JCLmonks.

After a bit of testing, s/\n/<BR>\n/g; seems to work fine. The users will actually start using this next week and I know something's going to go wrong, so I'll come back here and look at the other answers after they yell at me :)