Help! Oracle >> Excel97 Problem

Hi!
I'm in problem using ole Automation for Excel 97. I use oracle 7.3X and forms4.5.

I wanna activate a specific sheet(with index no. or sheet name). I will read/write data from/to the excel worksheet. In short, I wanna use excel as data Input and output method.

This is my code!! It doesn't work ^^:
Please help me!!

        application := ole2.create_obj('Excel.Application');

        ole2.set_property(application, 'Visible', 'True');

        workbooks := ole2.get_obj_property(application, 'Workbooks');
        workbook  := ole2.invoke_obj(workbooks, 'Add');

        worksheets:= ole2.get_obj_property(workbook, 'Worksheets');

        args := OLE2.CREATE_ARGLIST;
        OLE2.ADD_ARG(args, 'sheet2');  <-- I wanna activate sheet2
        ole2.invoke_obj(worksheets, 'Activate', args);
        OLE2.DESTROY_ARGLIST(args);