you can not import any excel file in Test director,you have
to   write directly.

YOU cant write test cases directly in test director you 
have to import from xl sheet


you have to add test director plug in
write test cases in xl sheet after that go to tools->launch 
testdirector like this

You can do in both the way either you can directly write in
Test Director or use excel Add Ins.

Yes we can write test cases directly to QC or test director
, go to test plan and first write in the summary, test cases
name, priority set and then move to 2nd pane or tab where we
can see excel sheet format . Here do write the test cases.


Other way is to import test cases from excel sheet to test
director or QC. For this we need to form  connection from
excel sheet to test director or QC via a plug -in connection.
Now go to testdirector and press import where we need to map
which column in excel sheet would be matching to which
column in test director excel sheet, so that only those
column will be moved.