http://msdn2.microsoft.com/en-us/library/f7s023d2.aspx
Its been ages since iv done VB but that link above would be a good starting point and looking on google i found a few sites with examples but i`ll let you do that your self

. I think basically you would have each button with an index and use that as the rnd instead of numbers so it`ll randomise between say 6 buttons and maybe a variable for when its chosen to be set to 1 or something...and then do an if statement to say if button 1 = true open form etc.
god i need to brush up on my programming me thinks