Apple today released Mini DisplayPort to VGA Firmware Update 1.0 for all Mini DisplayPort-enabled Macs.
This firmware update addresses intermittent flickering and compatibility issues such as no video on some external displays when using the Mini DisplayPort to VGA Adapter on your Mini DisplayPort enabled Mac.
Apple notes that in order to apply the update, the Mini DisplayPort to VGA adapter must be plugged into both the Mac and a compatible VGA display. The Mac must also be plugged in rather than running on battery power.
The update weighs in at 11.4 MB and requires OS X 10.5.6.