Apply group policy to multiple domains?

Hi All,

I have about 20 stores, all of which have their own independent domains going on (Server 2003).

All of the locations can see the corporate office network via a VPN connection.

I would like to be able to apply a group policy to all stores simultaneously. I’m sure there is a way to do this. How would this be done?

Add all the domains to the same forest? Is it possible to do this with a bunch of pre-existing domains? Can I apply group policy at the forest level? How would I join all my domains to a central forest?

Thanks.