Many games are available free.
Your interest in them will provide a source of amusement that need not be terribly expensive nor be frustrating, once you make the relatively easy insertion of a video card add-on to your PC.
It will provide an immediate shift of system memory utilization from the mainboard to the card.
Meaning if you now have 512mb RAM, monitor related functions probably grab 32Mb right off the top.
A card will restore that system RAM by shifting all monitor related memory-consuming tasks to it.
Cards function with their own RAM.
Some use their own 32mb RAM.
64mb is the next level.
128mb are more expensive.
256mb are even more capable (and expensive)
Any video card will improve your PCs graphics capability.
As Rimmer points out, AGP is a kinda standard.
AGP means Advanced Graphic Port.
The AGP slot is closer to the cpu than a PCI port (slot).
Meaning it uses a more specialized circuit interaction than a PCI one, which is designed to allow
device (card) interaction with the cpu for a wide variety of card types. Like modems & sound cards.
PCI Express is newer, and builds upon the advancing architecture of mainboard design beyond the AGP slot's "proximity" advantage. They are able to move more info from card to cpu quicker than the older types of video card/motherboard designs.
Hope you get something out of this.
Try this site for free games ....http://www.3dgamers.com/games/