I found this very very helpful, very indepth also - covers a lot of stuff. $45 is definatly worth the money.
Digital Tutors - Walk Cycle
check section 22 of the tutorial contents.
22. Bonus Lesson: Adding forward translation to the character so it moves forward
I will have a look at mine in a while and post a reply on how this can be achieved if you dont want to purchase it.
Hope this helps.