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.

Usage:

$ wget http://people.debian.org/~sthibault/hurd-i386/debian-hurd.img.tar.gz
$ tar -xz < debian-hurd.img.tar.gz
$ qemu -m 512 -net nic,model=rtl8139 -net user -drive cache=writeback,index=0,media=disk,file=$(echo debian-hurd-*.img)

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 root.

For more detailed instructions, please see the QEMU page.