The GT225 is said to be a 40nm shrink of the GeForce 8800 GS, which was rebranded to GeForce 9600 GSO and recently again to G130 for some OEM clients.
The GT220 is a derivative of the 55nm GeForce 9500 with higher clockspeeds, this part is currently available under the GT120 name for special customers.
The third 40nm GPU is the GT210, this is a shrink of the GeForce 8500, which was later rebadged to GeForce 9400 and then to GT100.