Just taken a crack at this.....
In standard situation, If IP is 192.168.0.x and subnet mask is 255.255.255.0, then the gateway is 192.168.0.1. This is lock due to your subnet mask, but I remeber somewhere that mention you can create a "host" file and save it in windows system folder to redirect the gateway traffic to a dfferent subnet. I think you should try to do some research on the "host" file.
