Test the sheet set order method
HSSFWorkbook wb = new HSSFWorkbook();
for (int i=0; i < 10; i++)
{
HSSFSheet s = wb.createSheet("Sheet " +i);
Sheet sheet = s.getSheet();
}
wb.getWorkbook().setSheetOrder("Sheet 6", 0);
wb.getWorkbook().setSheetOrder("Sheet 3", 7);
wb.getWorkbook().setSheetOrder("Sheet 1", 9);