Ping

I am not clear from your post quite what it is that you are attempting to accomplish. Is it a second gateway from the perspective of the PCs in your network (having a redundant router to establish connectivity if the primary router were to fail) or is it a second gateway for the router to use to have a redundant path to the outside?

If it is a second gateway for the PCs there is a simple answer: put the second router into the network and configure HSRP between the routers. With HSRP each router has its own physical interface address in the subnet and there is a shared address (or virtual address) that either router can use. You configure the PCs gateway address to be the shared HSRP address. In operation one of the routers becomes primary and uses the shared address and all the PCs send their traffic to the primary router. But if there is a problem with the primary router the standby router becomes active, takes over the shared address. This is quite transparent to the PCs. The PCs are still sending traffic to the same gateway address but now it happens to be on the second router rather than the first.

HTH

Rick

When you said another GW is that you mean you have another router? If yes you many need to Run HSRP and use the VIP as the GW in the PC, if you have one router connecting to ISP and LAN it?s a single point of failur,

please provide the topology details for better solution