Okay, I've tried using Xming and PuTTY, as well as Cygwin/X and Cygwin ssh, and it is not working.
I've been able to run X applications locally, so it's not a client-side X problem.
I've connected to the server using
ssh -X user@server
and ended up with this:
local-user@client: ~$ ssh -X user@server user@server's password: Last login: Sun Jul 19 15:26:46 2009 from 192.168.100.147 [user@server ~]$ xclock &  27770 [user@server ~]$ Error: Can't open display: localhost:10.0 + Exit 1 xclock [user@server ~]$ [user@server ~]$
Here's the relevant snippet of my sshd_config
#AllowTcpForwarding yes #GatewayPorts no #X11Forwarding no X11Forwarding yes X11DisplayOffset 10 X11UseLocalhost yes
I can't seem to find ssh_config on the client-side. /etc/ssh doesn't exist.