I used this as a starting point to get Xen running.
1. Install the base xVM
pkg install SUNWxvmhvm
pkg install SUNWvirtinst
pkg install SUNWlibvirt
pkg install SUNWurlgrabber
2. Configure GRUB (I did this step completely different)
pfexec gedit /rpool/boot/grub/menu.lst
add:
title ... xVM
findroot (pool_rpool,0,a)
kernel$ /boot/$ISADIR/xen.gz
module$ /platform/i86xpv/kernel/$ISADIR/unix /platform/i86xpv/kernel/$ISADIR/unix -B $ZFS-BOOTFS
module$ /platform/i86pc/$ISADIR/boot_archive
bootfs rpool/ROOT/opensolaris-1
3. Reboot into new configuration
4. 'uname -a' should contain 'i86xpv'
5. Startup the services
svcadm enable store
svcadm enable xend
svcadm enable console
svcadm enable domains
svcadm enable virtd
6. Make sure they are running
malachi@serveris:~# svcs | grep xvm
online 19:34:15 svc:/system/xvm/store:default
online 19:34:22 svc:/system/xvm/xend:default
online 19:34:24 svc:/system/xvm/console:default
online 19:34:29 svc:/system/xvm/domains:default
online 19:34:33 svc:/system/xvm/virtd:default
Now to figure out how to do the domU :)