Note: GNU Mach now handles PAE, so you can now use a PAE-enabled Hypervisor + dom0

- Copy gnumach-xen and hurd-modules to your dom0 /boot.
- Copy hurd into /etc/xen, edit it for fixing access to your hurd /, swap, and memory.
- Run xm create -c hurd, gnumach should get started.
- If xm complains about networking, it's Xen fault (or missing tools like
  bridge-utils, see Xen documentation for how to configure the network. The
  simplest way is network-nat.

If you want to generate these images, first get the gnumach-1-branch-Xen-branch branch from gnumach CVS, i.e.

cvs -d :pserver:anonymous@cvs.savannah.gnu.org:/cvsroot/hurd co -r gnumach-1-branch-Xen-branch gnumach

Then look for "Ugly" in kern/bootstrap.c, how to generate hurd-modules is explained there, and you'll have to fix EXT2FS_SIZE and LD_SO_SIZE by hand.  Then use ./configure --enable-platform=xen && make