when it comes to inputting my wireless key I get a key missmatch
You will have to be more specific about what you are trying to do. The home hub 3 is a router, so why would you want to plug in another one?
I use a netgear adapter in my desktop computer in another room from the hub, I thought that by using the Linksys I would get a better connection !! I get the key missmatch trying to connect
You cannot connect two routers to your broadband line. How is the Linksys connected to the home hub?
I think I can see what you are trying to do. You cannot use a wireless router to connect wirelessly to the home hub, as its a wireless access point and not a client.
If its a general networking issue that you are trying to solve, then there are some suggestions here.