Even with the extra core, I think you'll find the AMD chip to be slower. Mobile Phenoms do not have any L3 cache and performance-per-clock, AMD's current offerings are slightly behind the Core 2 CPUs, so a faster Core 2 is most likely going to be faster MOST of the time, unless you have something that uses that 3rd core really heavily.
Graphics-wise, I think the DX10 part will be faster. The Radeon 6650
has 480 shaders and a 128-bit DDR3 memory bus. You're most likely (though I'm not sure) looking at 8 ROPs, which does have a pretty big impact on framerate. You're looking at something marginally faster than a Radeon 4650 or 4670 (desktop) with DX11 features, which won't be useful when you're talking about something that slow.The Geforce
appears to be an 8800GT in terms of shader count, memory bandwidth, clock speed...everything. I think this is probably the faster choice for the near term. Well, probably always the faster choice until DX10 rendering paths go away entirely.
So faster CPU, faster GPU, more memory...I'd probably go with the G72 if I had to buy one of those two machines. Neither are going to be gaming monsters, even at 1600x900, but the G72 should be a better experience despite being older.