Making swf appear sometimes!

hey all,

just a thought but can this be done…

I need when a user visits the site a perticular movieclip loads, is there a way of making that movieclip only show a percentage of the time? like lets say only 40% on the time when a user logs on they will see this movieclip but 60% it will not even show?

any advice or help is much appreciated.

thankyou :}