Display World Coordinates In A Text Box?

At the minute I can display the mouse position using Cusor.Position.ToString() but my screen resolution is widescreem - 1360:768. What about about someone with a standard 1024:768? If I use my application on other computers, it won't work because it deeply depends on mouse co-ordinates

I am aware of a world coordinate system (or something) that will work on all screen resolutions. To use this (which I will need to) I will need to change all of my coordinates in the code? So I'll need to display it in a text box like I did with Cusor.Position.ToString() but what code can I use to get the world coordinate?

There is something like PoibntToScreen and PointToClient but what do these do exactly and how do I use them? I tried using

Code:
MouseCoordinates_tssl.Text = "Mouse Coordinates: " + "{X:" + PointToScreen(New Point(Cursor.Position.X, Cursor.Position.Y)).X.ToString + "; Y:" + PointToScreen(New Point(Cursor.Position.X, Cursor.Position.Y)).Y.ToString + ";}"
but much to my disappointment, it didn't work. What could I do that would work?