I have added a 2/4 time signature hopefully to add a 1/2 measure to my piece.  It appears that I can only add a 4/4 measure to my cuurrent musical piece.  Does anybody know how to add a 1/2 measure INSERT?

Assuming your MIDI resolution is set to the default 960 ticks per quarter note in Preferences, use Project > Insert Time/Measures and choose 1920 ticks.

In the words of Walter White, "No half measures."
 
However, here's how I'd do it.  Caveat: I'm not at my computer so I'm going to be going from memory.
 
Insert the 4/4 measure and slide everything over.
Insert a meter change at the new measure, changing it to 2/4
Insert a meter change at the beginning of the NEXT measure, changing it and everything after it back to 4/4
Slide everything around to line up again if needed.

You cannot add a half-measure, but what you can do is change the meter, which essentially accomplishes the same thing.
Let's say you're writing in 4/4.  Change a measure to 2/4 (or 4/8) and you now have "half" a measure. 
 
JG
www.jerrygerber.com
 

The method Craig describes will insert (and shift everything after the insert over by) 2 quarter notes, without changing the time signature, if that's what you want to do - but then everything after the shift will be shifted two beats from the bar lines, which may or may not be what you want. To get the bars to align, you'll need the time-signature changes to set up a single bar of 2/4.

subtlearts
The method Craig describes will insert (and shift everything after the insert over by) 2 quarter notes, without changing the time signature, if that's what you want to do - but then everything after the shift will be shifted two beats from the bar lines, which may or may not be what you want. To get the bars to align, you'll need the time-signature changes to set up a single bar of 2/4.

Right, I thought it was solely about inserting half a measure of time, not inserting a physical half-measure.

The best forum ever.
This is to all you guys helping this guy out.
 
Peace