Flash backgrounds

[COLOR=firebrick]I recently started using flash mx while doing a prject for a progamming class in school. I’m just doing basic stuff but i havent been able to find a certain answer to my question. I used to use future basic two and in there you can create a program in which random numbers pop up while a random background also appears. I tried modifying this so that the numbers would morph and the background would change but i cant figure out how to get the randomly changing background…any one have any idea???[/COLOR]