What are you trying to do? There's no way to determine a spatial reference given a set of x,y coordinates because the range of x,y values are not unique to a particular spatial reference. In other words, you can't say that because my point has coordinates 0, 0 that it is in the Nad 83 Utm Zone 18N spatial reference because a point whose coordinates are 0, 0 could be in any spatial reference.
"Setting the spatialreference property of the point does not change the x,y values. " This is correct. When you set the SpatialReference property on a point object you are specifying the spatial reference of the point, not performing any kind of transformation. If you want to project the point from one spatial reference to another then you should be calling the Project method. The point object will need to already have a spatial reference set on it before calling Project.
