It's fairly easy if you know how to configure a router. I use 4-5 routers in my house to extend wireless.
Figure out the IP address of the Linkysys router. Lets say it's the standard 192.168.1.1
Connect a PC directly to the LAN port on the Netgear router and go into it's configuration.
Setup the wireless on the Netgear for whatever password/ssid/security you want.
Turn off DHCP, and assign it a static IP. I usually try to number my routers after the first main one, so make it say 192.168.1.2 Once you apply these changes, you won't be able to login back in right away, that's fine.
Now plug the Netgear into a LAN port coming from the Linksys to a LAN port on the Netgear.
It should now be on your network, with it's own wireless and you can now log back in to whatever IP it was assigned if you need to confgure anything else.