I would definately go with dx10 only. By the time you've finished it, it'll be mature
DX10 only would also mean "it won't run on an non-vista machine", and currently there's still more people who DON'T run Vista than those who do...
DX10 only would also mean "it won't run on an non-vista machine", and currently there's still more people who DON'T run Vista than those who do...