Note: since GNU Mach doesn't handle PAE, you need a PAE-disabled Hypervisor.
Get the binaries [here](http://dept-info.labri.fr/~thibault/hurd-xen/).

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

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

The current hurd-modules was built from the debian packages hurd 20070606-2 and
libc0.3 2.6.1-1.