I have a created a custom player model with a custom walk cycle, but it is not linked to the movement of the character. Help?

I haven't done that myself, but my brother has. I think he exported chell, and used her bone structure. I suspect if you name your bones and bone structure the same as chells for each part, it should work.

You don't necessarily need to make the player model have chell's bone structure or animations, but your animations need to have the correct activity names. Go into hammer and take a look at chell's animations under the ACTIVITIES tab. These are the names (in all caps) that you need to give to the activities in your animations.

http://www.youtube.com/watch?v=B_NgKFRJ0pg