What Duality is talking about is your motherboard. Most good mobos support AGP x8, and models made from mid 2005 until now should all support PCI-Express x16. They're just slots to ptu graphics cards into. PCI-E is the best type you can have. My card is an ATI Radeon X1650 Pro 512MB PCI-E with DDR2. I get awesome graphics and frames in all of my games (except for DoD:S which most people have framerate issues with). Still get good frames in it, just sometimes a little lower in massive firefights in open areas. It was $217 I think.
You can't go wrong with nvidia. Though you'll be limited if you only have AGP which means you mite end up with something like Nvidia Geforce 6200, which is ok but very dated. My current is Nvidia Geforce 7650 GS which works perfect. I'm not sure about Radeons as I've never had one.
Well tell me what Processor you have and that might help narrow your requirements down... or if you have one of this pre-built HP, Dell, ect PC's just tell me the model (i.e. dimension 4800). And I can find the perfect card for that system.
Plus, are you saying you have $500 you're willing to spend or just $500 in general??
for games, nvidia by far. radeon is good but you have to spend A LOT of money to get a card that is of nvidia quality (in my opinion). up until almost a year ago i had radeon but now that ive seen what invidia can do. im not going back.
Source is a really picky and random engine when it comes to graphics cards. If you're going to buy an nvidia, and don't want to pay for an 8800, i'd recommend a 7600. For some reason, source works better with the 7600 than the 7900.
Also, I've heard that ati cards render source better, but I've never seen any proof of this. I still use nvidia.
Ok well... that doesnt narrow it down enough sadly, the Celeron D comes more often with AGP setup but can go into a PCI-e platform. Although its not exactly the fastest cpu and more than likely you have a small powersupply.
I need as much info here kid... is this a pre-built? is it a custom? I need to know in order to pick the card. Too powerful of a card and you'll be CPU limited or wont have enough wattage...
So whatever you can tell me about this system would help otherwise we're all spitting out suggestions that may not be possible for you.
Also with a system that has a celeron d 330 as its base means you're not gonna be able to go really hi-end or anything. But I should be able to get you decent performance for about $135 - $200.
Ideally I need to know about your motherboard and powersupply but that does tell me that with this $500 dollars you have you will GREATLY benefit but buying more memory along the new GPU. Only thing is you would need to know if thats 512mb in 1 stick or 2x 256mb sticks.
If its not a custom computer then tell me what make and model it is (i.e. HP Pavilion d6000y). That should give me all I need to know but I already have in mind some cards that'll fit but it all depends on your graphics slot and power supply wattage now.