Take the old card out. If it's on the MOThERBOARD, meaning there is NO CARD stuck to the AGP slot then you will have to disable the video-card in the CONTROL PANEL.

If not, simply take the old card out, put the new one in. Make sure its in there tight, and the screw has been placed on it. VID cards are picky whores who will act all funny if not properly in. One there, you can uninstall your old drivers (in the ADD/REMOVE PROGRAM and also in the SYSTEM-DEVICe MANAGER tab), and then install news ones, that correspond with your new card. Of course most nVidia drivers work with each other, but its always best to do a fresh install. Go for the 40.72's.