A VPN is about making a particular device look like it's on the target network, so I'm not sure you really want your n900 doping anything special if the point is getting your tab on the corporate network. The n900 is just providing your internet connection while you are on the road, much like your broadband connection at home would provide your corporate laptop an internet connection from home. Rather than modify your n900 connection at all, make the tablet do what you want it to do: go into settings > wireless & networks > VPN settings on your tablet and add your corporate VPN settings in there.