update: (07/08/2010) This method no longer works, however this does
Flash has an annoying habit of exiting full screen if you do any action outside of the window. This is most annoying if you have dual screens and want one to run a full screen flash video whilst doing something else on the other.
Over the last few years how to hex edit out this function has been posted online between versions. Most people to fix this have used the pre-hacked flash drivers however, these drivers over here have not been updated since April 2009 and no longer support Flash 10.
note: First try 'hack' as advised, I however had to first use the 'unhack' option, then 'hack' option to get it to work.