First to clarify AGP this is what a slot looks like with a card.
Okay first thing you do when you want to buy a video card is to get one that fits your needs. 9200se or 9250 both from ati will work but u can find out which nvida ones work if they are cheaper.
Step 1. buy a card
Step 2. go to the brands web site ( ati.com or nvidia.com) and download the latest drivers. (remember where you put them).
Step 3. go to control panle, then go to display, then go to settings, then click advanced, then go to adapter. click properties, at the bottem it will say this device is working properly. there is a drop down bar and it should say enabled, move it to disable. it will ask you to reboot now, click no, now turn off your computer. (if you would have clicked yes the it would restart your comp. what you would have seen would have scared you)
Step 4. unplug every thing from back of case.(not inside). Open Case.
Step 5. remove the screw and shield from case. insert card press down till it slides in.
Step 6. plug every thing back in. put the monitor cable in to the back of your new card. turn on the comp.
Step 7. let the comp load when the wizerd says you have a new device and it would like to install it CLICK CANCEL (i put it big because i made that mistake) (also the screen will look werid or distorted).
Step 7. install your drives that you downloaded earlyer by double clicking the icon. click next on every thing. when you get to the part of the install were it asks you to click { for ATI cards (basic or express dont remember) or advandced click the basic. countinue with install.
Step 8. it will ask you to restart your comp. now it will look normal agian. YOU ARE DONE
hope this helps.
EDIT: the cheapest card i found that will run the game is at circurt city the eVGA GeForce 5200 FX for $40 after rebates, it should run the game but i dont know how well. the ATI card are $70 and they will run the games pretty good.