I doubt that the GPU he chooses will allow him to play at any true HD resolutions. As I have pointed out in the past, increasing the internal resolution and/or applying AA+AF will decrease Dolphin's performance substantially - to a point where it begs the question if these things are really being offloaded unto the GPU.
Anyway, geforce6150SE you say? Would that be an nForce 4~ board you have (meaning you have a free PCI Express slot)? If so either card is fine, but sporting an nForce 4 MB would suggest that your CPU is going to be limiting your new purchase anyway. Might want to think about saving up even more and just buying a whole new system. Not just for Dolphin, but for everything else in general.
Anyway, geforce6150SE you say? Would that be an nForce 4~ board you have (meaning you have a free PCI Express slot)? If so either card is fine, but sporting an nForce 4 MB would suggest that your CPU is going to be limiting your new purchase anyway. Might want to think about saving up even more and just buying a whole new system. Not just for Dolphin, but for everything else in general.