Some help with RegExp, please

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";
?>

It returns everything. What i really need is to get the contents between <?
and ?>, and only that. I can imagine the RegExp is diung it right, because
ideed there are <? and, at the end of the text, another ?>, but it is not
clever enough to take the PHP UP TO THE FIRST COINDICENCE OF ?>, and so on,
and so on...

Can anyone help me? I would appreciate it very much.

Thanks anyway