Never mind what I said. You actually have to do a few things to unlock the "Brass Balls" achievement.
(If anyone was wondering on how to unlock it. Here's a TUT. Long but thorough.):
1.) Move saves to HDD.
2.) Delete the "Ryan Industries" DLC from your HDD. (Free to download)
3.) Clear you cache.
4.) Sign out, and sign in with another XBL account. (Silver or Gold is fine)
5.) Load up Bioshock, and update the game.
6.) Start a new game with the OTHER account. Select HARD difficulty.
7.) When the game actually gets to the gameplay, you will be prompted with a message about your DLC. Hit ok.
8.) As soon as you can, hit Pause. Go to Options, and check the bottom to see if it says "Disable Vita Chambers". If so, great so far.
9.) Now go back to the games Main Menu.
10.) Sign out of the other account, and sign back in with YOUR account.
11.) Load up the correct "Brass Balls" save.
12.) When it's loaded. Hit Pause, go to Options, and check if it still says, "Disable Vita Chambers".
13.) Turn it ON.
14.) Finish off final boss, and "Brass Balls" will unlock right when the cutscene starts.