One way to do it is to use Spreadsheet::WriteExcel:

    #!/usr/bin/perl -w

    use strict;
    use Spreadsheet::WriteExcel;

    my $workbook   = Spreadsheet::WriteExcel->new('test.xls');
    my $worksheet  = $workbook->addworksheet();

    my $heading    = $workbook->addformat(bold => 1);


    $worksheet->write('A1', 'This is bold', $heading);
    $worksheet->write('B1', 'This is not'           );
[download]

There are other ways to do it as well, most notably via Win32::OLE.

Have a look at cacharbe's Using Win32::OLE and Excel - Tips and Tricks.

--
John.