X11 Forwarding works on Windows with Xming and Putty, but not with ssh command line
Have you tried
ssh -X username@hostname xclock
Normally, the DISPLAY on the remote machine is not 0:0, but will be set by ssh automatically.
Also, Putty has a command line mode too, all you have to do is to add it's directory to your path and you can do
plink -X username@hostname xclock