When you transform a vector with a perspective matrix, you should use a Vector4 with the W-component set to 1.
Matrix m = Matrix.CreatePerspectiveFieldOfView((float)Math.PI / 2, 1, 1, 100);
Vector4 v2 = Vector4.Transform(new Vector4(v1, 1), m);
v2 /= v2.W;
The final division by v2.W is needed to get the perspective effect.