ubuntu 12.10 64 bit /tmp does not exist.......It also keeps bugging out.

1. first Open the Terminal (shortcut keys for opening terminal are Ctrl+Alt+T).
Just Login to your root account using su - command in the terminal. It will ask your root password and is different from your user login password. whenever you enter into root account the $ symbol at your command prompt will change into # . Example [bhaskar@bhaskar-Inspiron-1525:/$] this is my user login and it will change into [root@bhaskar-Inspiron-1525:~#] after entering into root account. Be careful while working with root account and it can damage anything in your ubuntu system.
2. in second step, you shall need to create a temporary directory i.e. /tmp inorder to work your Ubuntu OS. I think you deleted that tmp folder from your root directory. And this is the directory where temporary data will be stored by operating system.
3. Creation of /tmp folder by using following commands.

mkdir /tmp
chmod o+t,ugo+rw /tmp

first command will create a directory tmp under root(/) directory and second command chmod will change permission to your created temporary directory.

if you have any trouble follow the website given below and read carefully the concept behind this problem.
http://superuser.com/questions/241955/tmp-directory-deleted-i-cannot-login-to-the-system

use:

sudo -i

to get a root prompt. Su will not work as the root account is disabled and there is no password for it.

I think you may have to boot to a recovery terminal to execute those commands as by the sounds of it you are unable to get to the ubuntu desktop.