PHP is not evaluated

I feel that I am missing something extremely simple.

I installed the module for Drupal 6, have created an input type called PHP and have enabled code filter for that input type.

Then, I posted a page using that input type (so as not to have any conflict with other input types) with the following text:

print "Hello World";

and all it does is surround the php code with a grey box. It doesn't actually evaluate the code, which is what I need done for some event work.