XNA 4.0 requires a minimum of SM 2.0. So by default the users running your game will need at minimum 2.0 to run. If you need something lower than 2.0 then you should use XNA 3.1.
xna4.0项目默认设置是支持SM3.0，而gma950只支持到sm2.0。所以需要修改工程的属性。将Game Profile改为Reach就OK了。具体在代码级设置还没有看，估计也可以。