How to associate document files with MS Office 2010 Beta?

"not sure if this answers you question, but i had a similar problem of not being able to alter my default program settings for ms office programs, like you mention due to the virtualisation handler.
Instead of fiddling in my registry i chose to get rid of the virtualisation handler. To do so you have to deinstall and instaal some office programs, see detailed instructions at:
http://social.technet.microsoft.com/Forums/en/office2010/thread/0d2708ec-13d8-41dc-a62a-32792975801b
hope this helps."