domian access via wireless pc

I have a wireless pc that I want to connect up to a domain, but I want the connection to forced through a VPN.

Rundown of the network.
have a cable modem connected to a Watchguard Firebox SOHO w/ VPN. There is a hub and wireless access point connteced to the SOHO.

Is it possible to connect to the network throught the VPN and then login to the domain?

If not does anyone have any ideas on what to do?

Thanks,
Billy