Did it work before on this installation, or have you freshly installed Linux Mint 11 and has your Ethernet connection never worked on it?
Also, are you aware that Linux Mint 11 has been obsoleted and reached end-of-life in October 2012? http://www.linuxmint.com/oldreleases.php
. You'd be recommend to install Linux Mint 13, the current long term support release (support till April 2017), or Linux Mint 14, the latest release with the newest software (support till April 2014).