There are as many ways to do this as there are for people to actually walk.
This is one of the classic animation challenges - there really isn't a single solution. I would suggest that, as a start, you look at the following:
1. Walk methods associated with characters from "hebuilder" and "shebuilder". These are "pose" based. (Alice quite smoothly handles the move from one pose to the next - i.e., the "tweening.")
2. The walk method associate with the MadScientist." This uses the various turn, roll and move commands.
Also the Alice 2.2 beta gallery has a complete folder of walking characters that work in Alice 2.0.