Form Dropdown Validation

[eluser]Juan Velandia[/eluser]
Hello Everyone. Wich aproach would you use to validate this dropdown

Code:

$report = array();
$report[0]= 'Please Select';
$report[1]= 'Sales';
$report[2]= 'Products';
$report[3]= 'customers';

echo form_dropdown('Report', $report, '');

To make users to select something else than "Please select". Thanks in advance!