error message handling

I tried to send this before, so if I did, forgive me, but I don't think it worked last time .:) I'm trying to find a way to handle errors by number. For example, if I get a "directory already exists" error, I want to know what the number that is so I can check the return value on the function that gave the error. That made no sense. Lemme try again. Instead of getting the php-generated error message, I want to create my own so the user has a nice message instead of one that makes it look like I don't know what I'm doing. :) Any suggestions? Jason