AS3, MC follows mouse constant speed?

Hello, I am new for action-script, and I encountered a problem for making a simple game that character follow the mouse direction with constant speed.

and I found one of the thread from other forum is similar what I wanted, but it is action-script 2.0, and I don’t really understand the script.

here’s the thread that I mentioned:
http://www.actionscript.org/forums/showthread.php3?t=86675

here’s the link of his outcome, and I wish I can make similar to this in AS3.0:
http://jdittmer.free.fr/test/test.htm

thank you very much~