New row if a number of cells have been reached

I'm trying to make a table of iframes (2 per row) and I query everything, but whenever it prints, everything is on a row of it's own even though I only tell every second one to. I can't figure out why this is happening:

<div id="main" style="width:1000px;">
    <?php
        $query = "SELECT * FROM开发者_JS百科 scripts";
        mysql_connect("localhost", "root", "");
        mysql_select_db("scriptsearch");
        $results = mysql_query($query);
        $num = mysql_num_rows($results);
        mysql_close();
    ?>
    <table border="0">
    <?php
        for($i = 0; $i <= $num; $i++){          
        if($i % 2 == 0) //is this the second one? if so, make a new row
            echo '<tr>';
        else{
    ?>
    <td><iframe src="scriptpreview.php?id=<?php echo $i;?>" style="width: 350px; height: 230px;" frameBorder="0" scrolling="no">Your browser needs to support iFrames for this website.</iframe></td>
    <?php }if($i % 2 == 0) echo '</tr>';/*end the row*/ } ?>
    </table>
</div>`

Edit: I've tried Krynble's solution, but no matter how I modify it, it still doesn't show up how I expect.

There's an error in your loop.

Try this:

<?php
    for($i = 0; $i <= $num; $i++){          
    if($i % 2 == 0) //is this the second one? if so, make a new row
        echo '<tr>';
?>
<td><iframe src="scriptpreview.php?id=<?php echo $i;?>" style="width: 350px; height: 230px;" frameBorder="0" scrolling="no">Your browser needs to support iFrames for this website.</iframe></td>
<?php if($i % 2 == 1) echo '</tr>';/*end the row*/ } ?>
<?php if($i % 2 == 1) //close last row in case we haven't done it yet.
        echo '</tr>';?>

You should print the iframe unconditionally, not inside an else. Besides, the closing </tr> should be printed when $i is odd.

Other people have commented on the php/html part, let me focus on the query part:

Don't do this:

$query = "SELECT * FROM scripts";          (1) select all ?
mysql_connect("localhost", "root", "");    (3) don't connect as root!
mysql_select_db("scriptsearch");
$results = mysql_query($query);            (4) no check for errors?
$num = mysql_num_rows($results);           (2) when you only want 1 count?

Do this instead:

$query = "SELECT count(*) as rowcount FROM scripts";                 
mysql_connect("localhost", "user1", "password");
mysql_select_db("scriptsearch");
if ($results = mysql_query($query)) {
  $row = mysql_fetch_row($results);
  $num = $row['rowcount'];
} else { echo "error....." }          

You don't have an opening <tr> tag in your table. You need to have a table row before you can put data in it.