Network card not showing up

I will give you a few things to look for, but if they fail then you may have to look at your distribution's installation documentation. I am willing to bet that somewhere in there are step by step network setup instructions.

(As root)
1.) $ lspci

You should be able to find your card somewhere in there. Here is mine:

00:14.0 Bridge: nVidia Corporation MCP51 Ethernet Controller (rev a1)

2.) ifconfig

If your network is set up you will have an entry for eth0 (that is a zero at the end)
Again, here is mine:

Code:

eth0 Link encap:Ethernet HWaddr .... inet addr:192.168.1.3 Bcast:192.168.1.255 Mask:255.255.255.0 inet6 addr: fc80::415:68ff:fe1e:3774/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:872073 errors:0 dropped:0 overruns:0 frame:0 TX packets:1201217 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:326994619 (311.8 MiB) TX bytes:1203126776 (1.1 GiB) Interrupt:23 Base address:0x6000

If you do not have something like this then there are a couple things that could be wrong:
1.) Your ethernet card does not have the right kernel driver installed:

$ cd /usr/src/linux
$ make menuconfig
find your card and install it as a module or into the kernel
(if as a module, modprobe modulename and also add it to /etc/modules.autoload/kernel-2.6)

2.) Your network is just not configured properly. For most router setups:

nano /etc/conf.d/net (sometimes net, sometimes networking or of the like)
config_eth0=( "dhcp" )

make sure you have a dhcp client installed (I use dhcpcd)

you can also run the dhcp client manually for testing:

dhcpcd eth0

Once everything is changed you will want to run /etc/init.d/net.eth0 start (or sometimes just networking instead of net.eth0)

Hope this helps!