daily counter

Hallo!

I copied this from demo and filled it into my site (index.php):
<table border="0" cellspacing="1" cellpadding="2" align="center">
<tr>
<td> <font face="Verdana, Arial, Helvetica, sans-serif" size="1">
<?php echo date("D, j F Y"); ?>
<br>
<br>
Total Visits:
<?php echo $visits['total']; ?>
<br>
<b><a href="javascript:void(window.open('visitors.php','Visitors','scrollbars=yes,width=420,height=210'))" class="links">Visitors</a>
today: <font color="#CC0066">
<?php echo $visits['visits_today']; ?>
</font></b> </font> </td>
</tr>
</table>

On the site I can see this:
dMon, 11 November 2002
Total Visits:
Visitors today:

Whe I click on Visitors i see this in a small window:"Fatal error: Unable to open visitors.php in Unknown on line 0"

In "read me" I cannot understand anything because its my first try with php.
What means this?: Chmod these files: visitor.php - 755
ip.txt - 666
daily.txt - 666
total_visits.txt

I hope anybody can help me!
Thank you in advance!