I would not update firmware as a first step, that should only be performed once you are familiar with all the router settings and if you have issues with the current firmware.
This model is a good router, a bit aged but allows for third-party firmware to extend functionality, has external antennas, etc.
First, you will need two Cat5 cables, one connected to the router's WAN port going to the cable/dsl modem, and the other connected to one of the LAN ports going to your client PCs. When you power-cycle both the modem and the router, you will probably have connectivity on your client PC.
The router specs and its default IP address are available here:
http://www.speedguide.net/routers/links ... -router-36
Once your client PC is connected to the router, you should be able to access its admin interface by typing
http://192.168.1.1 in your browser. You should be presented with a login prompt, the username should be blank, and the default password of that router is: admin
You do not need to install any software/firmware, etc. to configure most routers.
Once you login, you will have to configure your wireless network security.