They already have an PHP interpreter.
http://php-compiler.net/doku.php
In your face! Haha, don't worry... You just couldn't bother to think outside your little box, which you've so happily decorated with little pink flowers, and now think is the best box there is.
That's where the .Net framework shines: it has MSIL!
Here's another cool language which enables you to extend the language itself at compile-time:
http://boo.codehaus.org/