This is a fairly frequently asked question inside Sun, and now that the biweekly builds are available outside Sun, there are probably more people who are interested. If you want to create a Boot Environment with a specific build (not the latest one) in OpenSolaris, here are the steps to use:
beadm create snv122 beadm mount snv122 /mnt pkg -R /mnt install pkg:/firstname.lastname@example.org bootadm update-archive -R /mnt beadm umount snv122 beadm activate snv122
Caveat Emptor and all that stuff. This recipe comes with no warranty, but I’d be glad to make it more accurate or up-to-date if you let me know of improvements.