PCI Graphic card for Tomb Raider underworld

Hi,
There are PCI slots in your Machine and one or two PCI-Express slots (one of which might be very short). Usually the Graphics PCI-Express slot is the one on top (right below the CPU).
In order to play Tombraider at a decent speed, you should consider buying a Graphicscard for about 100-120$ going to low will result in low framerates, going to high is not worth the money since graphics cards are becoming obsolete in a matter of 2 years or so...

so get yourself a decent PCE-E GraphicsCard and youll be all set!
Hope this was understandable =)