http://www.php.net/manual/en/function.exec.php
from the manual. you should try it some time.
read the explanation, then the comments...there a quite a few comments that discuss executing perl from php.
if exec() doesn't work for you, passthru() should.....but that's all discussed in the manual as well.
fopen() will most likely just spit your perl code out to the browser.
:o)
-dolphinsnot