To help some of you out who accidently updated their minecraft, I will post a version of minecraft 1.2.3 in this post.
Be sure to backup your minecraft files (not that much could go wrong).
HOW TO INSTALL:
Note: Make sure your minecraft is closed!
Download minecraft 1.2.3 (
http://www.mediafire.com/?l7g0v5wg08wi6ik ).
Go to C:\Users\YOUR USERNAME\AppData\Roaming\.minecraft\bin
Backup the existing minecraft.jar if you want to keep it
Place the file you downloaded in C:\Users\YOUR USERNAME\AppData\Roaming\.minecraft\bin
Start your minecraft