AGP x8 graphics cards usually are compatible with AGP x4.
When buying a graphics card stick with NVIDIA or ATI gaming models (i.e. do not buy MX cards for gaming). Your monitor will plug right into the back of your graphics card.
Models of Cards that are fine for games:
[size=2.5]NVIDIA:[/size]
GeForce 4 Ti4200
GeForce 4 Ti4400
GeForce 4 Ti4600
GeForce 4 Ti4800 (8x AGP)
GeForce FX 5200
GeForce FX 5500
GeForce FX 5600
GeForce FX 5700
GeForce FX 5900/5950
(Faster Ultra versions are usually available for all of the above GeForce FX cards, they show significantly improved performance within games.)
GeForce (6) 6800 GT
GeForce (6) 6800 Ultra
[size=2.5]ATI:[/size]
Radeon 9000
Radeon 9200
Radeon 9500
Radeon 9600
Radeon 9700
Radeon 9800
(These ATI cards come in SE, Pro, and XT versions, SE is slower but cheaper, Pro and XT versions are very fast compared to the original chipset.)
(Personally I wouldn't recommend the SE versions for these cards, they are too slow for games; for me anyway.)
These are the manufacturers that I trust buying from:
ABIT
ASUS
Gainward
Hercules
MSI
Sapphire
(Bold format represents the manufacturers I have bought from in the past.)
Hope this helps.