Vbs syntax for Ps

You will most likely need to use Action Manager Code to get that information.  There is no DOM method to get that that info.  I do not know or use Vbs for its only supported on windows.  The Action Manager  JavaScript code I have seen for that looks like this.

////// check for selection //////
function hasSelection(){
var ref = new ActionReference();
ref.putEnumerated( charIDToTypeID("Dcmn"), charIDToTypeID("Ordn"), charIDToTypeID("Trgt") );
var docDesc = executeActionGet(ref);
var hasSelection = docDesc.hasKey(stringIDToTypeID("selection"));
return hasSelection;
};

alert("hasSelection = " + hasSelection() );

You may be able to use DOM code to get the current selection bounds, if VBS has a way of catching errors.   If there is no selection I would think trying to get the selection bounds would fail. So if it fails there is no selection. If it works you know there is a selection and know its bounds.

// Save the current preferences
var startRulerUnits = app.preferences.rulerUnits;
// Set Photoshop to use pixels 
app.preferences.rulerUnits = Units.PIXELS;
try { 
	var SB = activeDocument.selection.bounds;
	var SWidth = (SB[2].value) - (SB[0].value);
	var SHeight = (SB[3].value) - (SB[1].value);	
	alert("'" + activeDocument.activeLayer.name + "' Selection Bounds\nTop Left "
 	+  SB[0].value + "X," +  SB[1].value + "Y   Bottom Right "  +  SB[2].value + "X," +  SB[3].value
	+ "Y\nWidth " +  SWidth + "px   Height " + SHeight +"px" 
	+ "\nSlection center relative to canvas " + (SB[0].value + SWidth/2) + "X," +  (SB[1].value + SHeight/2) +"Y" );
}
catch(e) {alert("There is no active selection");}
// Return the app preferences
app.preferences.rulerUnits = startRulerUnits;