I bought Master Lam's Walking Chi Kung when it came out in 2006. It is a great book, packed with different walking exercises. There is even one where you walk on the spot - The Stationery Walking of the Medics.
The first sections of the book focus on breathing, the Tan Tiens, alignment and movement before the walking exercise are presented.
I especially like the moving San Ti posture from Xing Yi and the Walking on Ice exercise.