A Toolbar with an Excel button:

* Init method
This.ADDPROPERTY('oXL',CREATEOBJECT("Excel.Application"))

* Click

lcFile = PUTFILE('Save the query as an Excel worksheet','','XL5')
IF NOT EMPTY(lcFile)
        SELECT (THIS.ExportFile)
	EXPORT TO (lcFile) TYPE XL5
	WITH This
		.oXL.Workbooks.OPEN((lcFile))
		IF .oXL.VISIBLE = .F.
		     .oXL.VISIBLE = .T.
		ENDIF 
	ENDWITH
ENDIF

This creates a new instance of Excel, where I'd really just want to add
file2,... aso. to the exisiting instance.