That's because it is a fairly old socket. Since then, there has been Socket 754, Socket 939, Socket AM2, and Socket F, the most familiar being Socket AM2. If you still want to keep your graphics card and DDR memory, one option would be to upgrade your motherboard and processor to socket 754, which still uses DDR memory and the AGP slot. You might be able to find a Socket 939 motherboard with AGP, though it mostly uses PCI-express.