first, I didn't know you could forward x through putty, don't you need another program like xwin or exceed?
from the faq at
www.openssh.org :
2.7 - X11 and/or agent forwarding does not work.
Check your ssh_config and sshd_config. The default configuration files disable authentication agent and X11 forwarding. To enable it, put the line below in sshd_config:
X11Forwarding yes
and put the following lines in ssh_config:
ForwardAgent yes
ForwardX11 yes
NOTE: For users of Linux Mandrake 7.2, Mandrake modifies the XAUTHORITY environment variable in /etc/skel/.bashrc, and thus any bash user's home directory. This variable is set by OpenSSH and for either of the above options to work, you need to comment out the line:
# export XAUTHORITY=$HOME/.Xauthority