Should read up on these tuts:

http://www.flash-mx.com/flash/progressbar.cfm
http://www.macromedia.com/devnet/mx/flash/articles/tweening.html
http://www.actionscript.org/tutorials/advanced/Tween-Easing_Classes_Documented/index.shtml
http://www.timwalling.com/actionscript/32/mxtransitionstween-extended/

http://livedocs.macromedia.com/flash/mx2004/main_7_2/wwhelp/wwhimpl/common/html/wwhelp.htm?context=Flash_MX_2004&file=00002429.html