Apple released Mac mini EFI Firmware Update 1.2 on Monday. The update is designed to improve compatibility with Apple's latest memory kits.
The updater adds and application called Mac mini EFI Firmware Update.app to /Applications/Utilities. The updater applications should launch automatically once the download completes to begin the firmware update process.
Mac mini EFI Firmware Update 1.2 requires Mac OS X 10.5.7 or later. It is available via Apple's Software Update application or as a downloadable installer at the Apple Support Web site.