I have an ATI Radeon X700 AGP Pro 256, 179.99. I can play everything on high settings with this card of course it will depend on your overall system.
Ok first off...do you have AGP or PCI-express? If AGP, what speed is it...4X or 8X? Second, Your system isn't going to hande 3D games very well. Celeron's are the worst CPU's for gaming. Your RAM should be at least 512MB if you plan on playing games(1024 recommended)