Socket 478 is a long dead platform that was around before dual cores started to enter the market, you wont find any dual or quad cores on that platform.
To be honest, you wouldn't be able to upgrade the rig in any significant way without requiring a whole new build. A new CPU will require a new mobo, which will require DDR3 RAM, SATA HDD and optical and a new OS. If gaming is what your after you will need a decent GPU. Chances are you would have to get a new PSU to support this new hardware.
You might just have to settle with a console.