Shareing two internet connections on the laptop running Windows XP

You can do this with a static route

Details for how to do this can be found here http://www.ubuntugeek.com/howto-add-permanent-static-routes-in-ubuntu.html

You will define one route for your internal network to whichever interface that is attached to, and then you'll set the default route (0.0.0.0/0) to the other interface.

From the ForceBindIP page here (last updated in 2009):

As of version 1.2, all known functions in WS2_32.DLL that either explicitly or implicitly bind to an interface are intercepted. Please note however that certain programs may still end up using the default interface if they implement connections that do not use the standard winsock functions.

So unless you can be sure your program is using "standard" Winsock calls, then you can't be sure if it will work with ForceBindP.

You may want to try it with a few different programs and see if you get better/different results.

Also, keep in mind that ForceBindIP was never tested beyond Windows 2003 (at least not according to the page) so it's compatibility with newer Windows versions probably isn't guaranteed. :)