Take a look at this animation of a girl walking done for American Greetings.

This is an example of how a walk can be done quite simply in flash.

Each element was created separately in Illustrator and then imported into Flash. These are then made into separate movie clips.

In order for the legs to move in a smooth arc once they are tweened in flash, move the centre point of the movie clip to the top of the legs. This is the fulcrum point from which the legs need to swing.

Give the whole clip a slight up and down motion.

Once the main walking action is established, secondary animation on the hair can be added.

Finally, animate the background making it move from right to left in order to reinforce the illusion of motion.