In addition to Hilmar an Tore, you can also use GETFILE() to assign your textbox value:

* You could place this code in your textbox's Rightclick 
lcReturnFolder=SET('dire') && Save the current directory
lcXLSFileFolder="d:\bills\aar" 
CD (lcXLSFileFolder)
this.value=GETFILE("XL?","Select Excel FIle","Retrieve",0)
CD (lcReturnFolder)