I've worked quite a bit with OLE and excell though not through perl, and the best I've been able to come up with for this problem is to iterate down the rows, checking for an empty value in a column that you know will be filled, and thus building a totalrows scalar.... ie.

my $test;
my $totalrows = 1;
for ($test=$worksheet->Range("A$totalrows:A$totalrows")->('Value');$te
+st ne "";$totalrows++){
     $test=$worksheet->Range("A$totalrows:A$totalrows")->('Value');
}
$totalrows--;
[download]

This should give you the total number of rows with information. In VBA I would be checking for a Null value rather than an empty string, but I'm not sure how to do that in Perl, and I believe this should work (untested).
If someone knows how to check for a Null value in perl (not the same as undefined.) let me know.
This code snippet is based on the understanding that your current code works and is correctly using OLE for Perl.