theres this thing called google, i've found to to be pretty halpful..
http://www.dur.ac.uk/its/services/network/lan/install_network_card/
that will solve your problem of how to put it in. dont bother getting a tech at your computer shop to put in in. sereiously, the only reason you would do that is if you cant hold a screwdriver steady or if you're retarded and can't follow instructions.. save the money, do it your self and get yourself a new set of poles.
As for the card you will want a PCI 10/100Mbps card. You will be able to get the card from any computer part shop. I just had a look and i can get on $15 new zealand so they should be the same or less wherever you're from.