The Dimension 8200 has AGP 4x graphics that run max 32 bit @ 66MHz. It has a 172 pin, 1.5v slot. It can run in 2x or 4x mode.
All of the cards in the class you are looking at are Universal - meaning they will switch voltage to work in the slot. But a card that is designed for 3.3 volt may not perform well at 1.5v, so you should avoid these if you can if you are going to attempt Windows 7 on that machine.
From the PlayTool
"One practical matter which must be considered is the fact that some of the original AGP 1.0 motherboards do not provide enough power to operate some newer AGP video cards reliably. For example, some of the original motherboards using the first chipsets which supported AGP (like the Intel 440LX and 440BX) can become unstable if you install video cards which draw lots of power through the AGP slot. The motherboards can't always supply the necessary current for the newer video cards. So if you're adding a video card to an AGP 1.0 motherboard then it's a good idea to install a video card which doesn't consume very much power."
The Vista drivers
for these older cards will run as well as can be expected under Windows 7. Just use the most updated one on the nVidia or ATI website. It can be a try and see process.
I've refurbished two 8100s and can tell you that that class of PC is getting really long in the tooth. The 8200 wasn't much of an upgrade from those. I don't think that I would spend a lot of money trying to carry that beast along for too long!