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