Question : How to forcefully apply the Group policy to all the computers in  SBS 2008 environment ?

 1) How often are the group policies applied to all the client computers in SBS 2008 network ?
     All network computers are Windows XP

2)  Is there a setting which will define the interval time ? if YES where is it ?

3)  Can we force to apply the GP updates to all the network computers from the server itself ?

Answer : How to forcefully apply the Group policy to all the computers in  SBS 2008 environment ?

It's called bridged mode or WPS and not all software within routers support it.  Depending on the model of the router it is possible to install 3rd party software that does bridging very nicely.  Sveasoft and DD-WRT both have support for numerous routers.  The advantage to having a bridged network is that the reliability goes up.