Portable Cygwin works, but XWin fails

[fergus@bonhard.uklinux.net]

> What is your display variable set to?

localhost:0.0

> Do you have a /tmp/.X11-unix/X0
> file on your memory stick?

Yes: so I wonder whether in trying to make a CD version, as well as
re-routing the file /tmp/XWin.log, I ought also to try to re-route the file
/tmp/.X11-unix/X0.

But: the trouble seems to occur earlier, at the point that XWin atempts to
make the directory /tmp/.X11-unix. Can I trick XWin into creating this
elsewehere (i.e. somewhere writeable?)

Fergus