You should be able to do it as long as you have the networking chops to set it up. The Slingbox won't be the problem, clearing a path across the subnets is the trick. If you can set your routing tables up so two computers can see each other given the same senario, the Slingbox will be a breeze.
No internet = No problem, but you'll lose the SlingID service. When you add the Slingbox to the Player's directory, you'll have to configure the location manually with an IP and Port.
I would avoid the Web player for this application, use the full standalone program instead. Versions for Mac OS X 10.3+ and Windows are available.
Hope this helps,