I want to open the Unit of Measure window. When I call the Open method, the window opens but it has no data in it.

Dynamics.Forms.IvUofMLookup.Open();

What do I have to do for the window to fill up with data? 

If you were doing this in Dynamics, were is the window? How would you open it manually?

 Generally, the key is to populate the key field after you open the window. Also, there are methods that you can call to open the window directly and pass a pameter

See:
http://vstoolsforum.com/forums/p/67/135.aspx#135

It's not documented very well, though, that's why we have this forum. Please, if you find answers, post them here. Not just for this question, but anything the community might use.

Ok, I did it.

Finally the inventory UofM window is filling up with data.

There isn't a method to open the window and directly pass the parameters (like the sop window).

What I did was to fill the UOfMSchedule property:

                Dynamics.Forms.IvUofMLookup.IvUofMLookup.UOfMSchedule.Value = "Each";
                Dynamics.Forms.IvUofMLookup.IvUofMLookup.RedisplayButton.RunValidate();
                Dynamics.Forms.IvUofMLookup.IvUofMLookup.PullFocus();

Then I called the RedisplayButton to refresh the window.

That's it. 

Excellent. Pease remember to come back here and document your future successes for the community - we all need the help.