Simple Question: Case sensitivity

This is probably an easy question for most but here goes:

I am using PHP3 and postgres 6.5

I am trying to do a search on a peoples database and it works fine except
for the fact that I want to make it case insensitive as some in the database
are Smith and some are jones.  Is this a scripting thing or can it be done
in my query.

Here is the query:

$sql = "select surname, firstname, title, company, worktel, ext, hometel,
mobile, email, emailtwo from employees where firstname like '%$criteria%' or
surname like '%$criteria%'";

Thanks in advance,
Abe