My GUI contains a label PLease select workbook.. To select Workbook click on browse button...(After clicking the browse button user should be able to select excel workbook from the window..it will be a normal browse window like in our computer.)

Next label is select worksheet u wish to eamil from the following...
NOw all the sheets from the above selected workbook should be displayed in this textbox.I have made textbox size large enough so that 5, 6 sheet names can be displayed one below the other.