To enhance my wireless speeds Verizon suggests that I purchase the GigE Wireless router. Does this router Piggy back the current router already installed or does it replace it?
in general it is going to replace it. Follow these instructions to do so.
or run the CD and it will do it for you.
Also since you purchased it, then that means you get to keep both. There are several cool things you can do with two fios routers, so here is one of them.
would have to know your set up and what you want to accomplish to get more specific. :]