I want to upgrade my ATI Radeon 9000 Graphics Card?

I have a very old computer (HP Pavilion 700) With a not as old graphics card. I got this card installed about 8 or 9 years ago ( i originally bought it to play the first spiderman movie game). I want to upgrade it for I am interested in pc gaming once again. All I am wondering is would i need anything to get a more up to date Graphics card? I was looking at Nvidea geforce gtx580 or one of the ATI HD series.I'll probably go cheaper but i just wanted to know if i needed any extra hardware along with the graphics card.