Well if both domains are on the same server yes it is possible.
However you will not want to do this at all since your users would never be logged into Photopost. Your
vb navbar will always show you logged out when going to the photopost domain and if you try and login it will authenticate you and create the
vb cookies which will be the other domain so it will make the application useless.
You best bet would be to if you want them on separate domains to mock the forum stylesheet and header the best you can using regular html header footers.