Please I will like to require an assistance on how to build a router using network interface card. Your assistance will be highly appreciated...
Mostly you just build a really cheap, low power PC with Ethernet ports and a Wireless card if you want that and install PFSense or something of it's kind.
These are some other options as well:
http://www.ipfire.org/
http://www.clearfoundation.com/Software/overview.html
You will want 2 ether net ports one for WAN in and the other for LAN out and that will go to a switch and/or a wireless access point.
like an amd am1 apu with an intel nic? but you don't have wifi then right?
Totally with what Zibo said, go cheap as possible, use an old crappy PC if you have one, add some network cards then spend some time on the PFSense GUI getting it set up properly. The caching thing is so awesome for windows updates and the likes, especially if you're lagging behind in the internet download speed such as myself.