Here are the two Nvidia chips! They occupy a significant amount of the logic board. There's no way both of these puppies could fit in a MacBook Air.
The first chip is marked 37N3C2 0836B2 PB6623.S03 MCP79MXT-B2. This is the GeForce 9400M, also serving as a northbridge.
The second chip is marked U807B034 0827C1 NH7962.01W G96-632-C1. This is the GeForce 9600M GT, which has 32 processor cores and is capable of 120 Gigaflops.