Sorry this is a little late in coming, but here's how to check the read only flag.

use strict;
use warnings;
use Win32::OLE;

my $xlsFile = "c:\\temp\\myexcelfile.xls";
my $excel = Win32::OLE->new('Excel.Application', 'Quit');
my $book = $excel->Workbooks->Open("$xlsFile") or die;
if($book->{ReadOnly}+0 > 0){#the funny +0 is an easy way to force the 
+scalar to be interpreted as a number
  warn "$xlsFile is open Read Only!";
  $book->Close;
  $book = undef;
  $excel = undef;
}
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