Mo, First you need to hava a macro to open the other workbook. You can do this by selecting Tools-Macro-Record New Macro. Then give the macro a one word name. Then go ahead and open the worksheet you want. When you are done, go back to the original sheet (should still be open) and click the stop recording button. Now you have a macro that will open the other sheet. To ad a button, all you need to do is right click on the menu at the top, and select the Forms Meun. Click on the button icon. Then Click on your sheet where you want the button, hold and drag until the button is the size you want it. When you release the button, it will ask you to assign a macro. You can then click on the macro that you just recorded.
Good Luck