How can I recover from a corrupted blkindex.dat on Ubuntu 12.10?
On Linux, the Bitcoin client data is kept in the .bitcoin directory in your home directory. Go to ~/.bitcoin/ and you'll see the files in there. You may need to toggle Show Hidden Files in your file manager in order to see the directory.

If you remove blkindex.dat, the client will have to redownload the blockchain. I just tested this locally by moving my copy of the file to another file name temporarily - the client resync'd.

Since your copy of the index is corrupted apparently, it sounds like you need to delete it and resync.

A note: be careful to do not erase your wallet.dat. I recommend you back it up before. Your wallet.dat is your private keys.