copy values from a worksheet to another workbook. source workbook name unknown

I need to copy a range of values (actually two ranges). The ranges are of fixed size. Le't say A2:D20 and E2:H20.

Both workbooks have the exact same layout, and they both have the same named worksheet (in this case it's called Entry). However the actual filename of the source workbook is unknown. I know numerous users have changed the filename of the xls file.

I want to instruct them to open the old and new workbook, and open a third workbook containing the copy macro, they run the macro and it copies the data.

How can I reference a known worksheet name but of an unknown workbook name esp when the source and destination share the worksheet name?