nethermind

Download the minecraft 1.1 files here http://www.mediafire.com/?o202e8o6xl9dx2c.

Search for the file %appdata%
There should be a file called .minecraft and open that in there there is a file called bin.
Extract the file you have just downloaded and move the folder called bin into your .minecraft folder.
Finally, Merge it with the original bin folder that is already in your .minecraft folder and allow it to replace all of the files.

Make Sure Your Minecraft Is Closed When Doing This!

For Mac users
Go buy a PC, then follow the instructions above.