What motherboard do you have? AGP, and PCI-E was both very common in the old DDR days with Athlon X2's. Knowing the mobo can help us give you some ideas for GPU/RAM upgrades.
Your CPU is actually right below minimum specs, but you can find cheap replacements that would bring you into spec. RAM is above spec, and your GPU is just below minimum.
I can't really give good advice since I don't shop around much anymore, but it will boil down to exactly what motherboard you have. Use CPU-Z to get the motherboard model.