url and form text box value

[hd65]

I have 2 frames the top frame displays an jpg file (the url of the frame is the path and file name of the jpg). the bottom frame has a form with a hidden text box. I need to set the value of the text box to the url of the top frame each time the bottom frame is reloaded. I can set a variable to the url like this
var img = parent.imageside.location.href
but I can't set the text_box.value to the var img ????????
any help would be great.
thanks paul