there are several tools.
Adobe Flash CS3 will do it for you.
If you don't have Flash CS3 or another professional
application like Sorenson Squeeze consider a shareware application
like VisualHub (just do a Google search for VisualHub and you will
find it). VisualHub is shareware and therefore cheap (about $22
USD).
There are most likely freeware apps that will convert the
file(s) for you as well. Google is your friend. There is an
open-sourced command-line tool as well called ffmpeg (i think);
Google that and if you are comfortable at the command line you
should be able to install and use that and it would be free.
Best of luck