Doctor Twe offers some helpful explanatory material, including:

Long Division in Binary
http://mathforum.org/dr.math/problems/jindani.6.6.00.html

which links to

Binary Subtraction
http://mathforum.org/dr.math/problems/houston.7.25.96.html

Complement of a Number
http://mathforum.org/dr.math/problems/steve.7.10.96.html