Help with ereg()

Hi all. I'm trying to deal with Regular Expressions, but somehow it is
getting more difficult. I´m trying to do the folowing:

Read a text and get all of the PHP code out of it, highlight it and then
print all in nice HTML. I'm using this to get the PHP code:

ereg("<\?.*\?>",$Text,$PHP_code);

It works, yeah, but on a situation like this:

<?
    echo "aaaa";
?>
This is some other no php code
<?
    echo "this is PHP";
?>


Thanks all. I think this post is somewhere in the list, with another
subject.