That error most likely means pear is not installed on that server.
Are you sure you need to set the smtp server when applying? On most servers you can leave that field blank. Who do you host with?
I'd try using mail with the server field blank and then add the error message to the page if it doesn't work properly. If you need authenticated mail, which is extremely uncommon and unconventional in most cases, then you should be able to use Pear, but you need to make sure it is installed on your server.