So the new imac 20" doesnt have the gpu soldered? Would I be able to upgrade to something like the ati 4850 on my new 20"? I got a great deal on it since I work for GeekSquad so I dont mind shelling out a little to get some decent performace out of it.
No, you cannot simply take the card out and upgrade it, it still is a laptop part that uses an MXM-slot -- and even on PCs they don't always upgrade easy, according to the MXM-upgrade site.
Easiest to use an Apple part, since there are drivers for those, and they will fit it you use the other choice for the heat pipe.
And there is the rub, the GPU cooler likely will be different between the Nvidia generation machines and the Intel chipset generation. Probably would need somebody to image the differences between the two cards and mill the current 2007 heat pipe and/or add a conversion plate.