Case Insensitive Searching?

I am working on a project where I am creating a PHP front end to a Postgres
database. The schema is new but the data is old. Meaning I had to convert
the data from the old Informix DB.

Anyway all of the existing data is in all upper case. However new data going
in will be in both upper and lower case.(As requested by the customer.)

So the question is, how do I perform a case insensitive search? Is there a
DB setting I can set to ignore the case?

If not, then an example of some PHP code that can do this would be of a
great help.

Thanks,

Ben