How to get the Monitor Pos. in a Virtual Desktop

Hi everyone,

I have set a virtual desktop of 2048 * 864. My monitor resolution is
about 1152 * 864.
How can i get the PRESENT monitor position?
There must be an API or so because the OpenDialog shows consideration
for this and opens in the middle of the MONITOR POSITION!
However a form with the property Position = poScreenCenter opens in the
middle of the VIRTUAL DESKTOP!

Thanks for help,
Pat