Ethernet card

[Whickerman]

How would I know if my pc has a 10/100BT Ethernet card installed?

[j2buttonsw]

I would look in the device manager under network adapters

[vehelpfulguy]

Or have a look at the back of your PC to see if you have a socket like this in the picture (not a great picture but best I could find)

http://www.balliol.ox.ac.uk/comp/ethernet/rj45 _rj11.jpg

You need a socket like the one on the right. Note the icon above it, that may also be there, or it may say RJ45 or ETHERNET.

Do not confuse it with the socket on the left which is for a phone line and modem.

Often a PC wil have them next to each other.

[vehelpfulguy]

Here are some better pictures

http://www.publicwebstations.com/howto/etherne t.jpg

http://cableorganizer.com/images/cat5e-jacks/c at5e-RJ45-couplers-2.jpg

[stevie21]

Ethernet is the same shape as a modem socket but bigger so you can either just look at the back of your PC or right click My Computer + choose Properties.
Under the "Hardware" tab click "Device Manager" and look for "network adapters" as j2buttonsw said.