I'm not sure exactly what your problem is - starting Excel, opening the file or entering data - and obviously I don't have your "smoke test" file. Amending the code to create a new spreadsheet, this works on my system:

use strict;
use Win32::OLE;

#$doc = 'Smoke_Test.xls';
#$ex = Win32::OLE->GetObject($doc);
my $ex = Win32::OLE->new('Excel.Application');
$ex->{Visible}             = 1;
$ex->{SheetsInNewWorkbook} = 1;

# get a new workbook
#$book = $ex->Workbooks->Add;
my $book = $ex->Workbooks->Add;

# write to a particular cell
#$sheet = $book->Worksheets("Sheet1");
my $sheet = $book->Worksheets("Sheet1");
$sheet->Cells(1,1)->{Value} = "foo";

undef $book;
undef $ex;

exit(0);
[download]

It works just as well without the "undef" commands.

Regards,

John Davies