There is a QEMU image with Debian GNU/Hurd pre-installed available as http://people.debian.org/~sthibault/hurd-i386/debian-hurd.img.tar.gz.
$ wget http://people.debian.org/~sthibault/hurd-i386/debian-hurd.img.tar.gz $ tar -xz < debian-hurd.img.tar.gz $ kvm -m 1G -drive cache=writeback,file=$(echo debian-hurd-*.img)
Please also read the README file: http://people.debian.org/~sthibault/hurd-i386/README
If you have troubles extracting the image, you can use the gz version http://people.debian.org/~sthibault/hurd-i386/debian-hurd.img.gz, the zip version http://people.debian.org/~sthibault/hurd-i386/debian-hurd.img.zip, or even the plain version http://people.debian.org/~sthibault/hurd-i386/debian-hurd.img (3GiB!)
See the discussion about writeback caching.
Just in case you were wondering: the root password is empty.
For more detailed instructions, please see the QEMU page.