There are some very simple instructions here for dual booting with Windows 7 beta:
http://www.vimeo.com/2778519
However, I find this confusing as elsewhere I have seen that Windows 7 beta is only available as an upgrade option from Vista SP1.
Anyone know the real deal??
I would caution you that if you are able to get the full version (available only to those who have either a technet or msdn subscription) that it is a beta and could have unexpected behavior(s) that you make a dual boot unpleasant, but would increase the adventure factor. I would instead use either virtual server 2005, VPC 2007 (both are free) or a VMware client.