I just spent entirely too much time trying to find the git-init template directory on my Windows machine (so I could copy my default hooks from one machine to another).
In order to save this hard-won information to non-volatile memory (i.e. the Internets), here it is (at least for windows 7):
C:\Program Files\Git\share\git-core\templates – on a 32-bit OS
C:\Program Files (x86)\Git\share\git-core\templates\hooks – on a 64-bit OS