I aim at 1GHz CPU with like XP and 256MB of RAM and a 32MB Video card. Also test it on an old laptop as their GPUs mostly stink. The end speed will depend on a) if you are making a CPU heavy game and/or b) if you are making a graphically intensive game. For example, maybe your CPU doesn't do much but you are using lots of big graphics - the GPU will be the bottleneck. Or maybe you have some really complex slow logic code so the CPU is the bottleneck. Or maybe you are making tons or particles, this consumes a lot of CPU power and also GPU Power (this is pretty much like my match-3 games).
If the user has Vista, in theory the CPU is better and so is the GPU (if they bought it new and didn't upgrade a crap machine), but there were some awfully cheap and nasty low RAM Vista PCs/Laptops floating around when Vista came out.
If the user has Vista, in theory the CPU is better and so is the GPU (if they bought it new and didn't upgrade a crap machine), but there were some awfully cheap and nasty low RAM Vista PCs/Laptops floating around when Vista came out.