Tracy,

I have had success with the following...
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* Putting the top left corner in the center of the screen...
Wait "Please Wait..." window at (sysmetric(2)/fontmetric(1))/2,;
(sysmetric(1)/fontmetric(6))/2
* And to approximately center it, subtract half the size of the window...
Wait "Loading..." window at ((sysmetric(2)/fontmetric(1))/2) - 2,;
((sysmetric(1)/fontmetric(6))/2) - 8 nowait noclear

HTH