The iMac MXM Update
improves video compatibility with Boot Camp on certain 24" iMac models.
This installer places the iMac MXM Update firmware updater in the /Applications/Utilities folder on your computer. Run the updater in the Utilities folder to install the update. Updating takes only a few seconds.
To learn more about this iMac MXM Update, visit: http://docs.info.apple.com/article.html?artnum=306790