you need to be a little more specific, like what OS are you using ? are you using dial-up for internet access ?
if you just want to hook-up to the internet via the phone jack, just plug it into the phone jack slot on the back of your computer. then it's a matter of having the computer make a connection your internet service provider. either your ISP cd, or the downlowded browser you will be using.
What OS are you going to be using.? also you don't need to buy anything as long as you have enough phone cord to go from your modem card to the phone jack.