Well, I'm too lazy to count 145 lines right now (or cut-and-paste into a text editor), but my guess is that somewhere along the way you've forgotten to escape one of your quotes.
I would recommend you don't use PHP for such a huge block of HTML. Then you don't have to worry about PHP parse errors at all in there.
To play Petraverse, you are required to register for an account. This
process takes just five minutes and is totally free.</p>
<p>Please complete the registration form below. Fields marked with an
<font color="#FF0000"> <strong>*</strong></font> are required.</p>
<form action="register.php" method="post" name="register" id="register">
<table width="500" border="0" align="center" cellpadding="3" cellspacing="0">
<tr bgcolor="#FFFFFF">
....
<input type="username" value="<?php echo $username?>">Just to show how.
Incidentally, if you're going to use PHP, consider cutting down on the size of your code by e.g., using a loop to generate your <select> options.
EEewwww!!! <font> tags!!! Hck!Ppptt! Please! Ick!