I know this may be an old link to some of you but I thought I would throw it out there anyway. This seems to be a pretty decent read so far. The foreword is written by Ward Cunningham so it obviously can’t be too bad!.
http://www.microsoft.com/downloads/details.aspx?FamilyId=3C81C38E-ABFC-484F-A076-CF99B3485754&displaylang=en