I just put up a simple guestbook script. when I access the page it gives me post errors:

Notice: Undefined index: post in C:\Program Files\Apache Group\Apache2

what does this mean?

<?
if ($_POST["post"])
{
 	 if ($_POST["name"]=="")
	 {
	 }else{
$file=fopen("guestbook.txt", "a+");
$today = date("F j, Y, A");
$entry="Posted on:  ";
$entry.=$today;
$entry.="\n";
$entry.="Name:  ";
$entry.=$_POST["name"];
$entry.="\n";
$entry.="Email:  ";
$entry.="<a href='mailto:";
$entry.=$_POST["email"];
$entry.="'>";
$entry.=$_POST["email"];
$entry.="</a>";
$entry.="\n";
if ($_POST["homepage"]=="http://www."){$_POST["homepage"]="";}
$entry.="Homepage:  ";
$entry.="<a href='";
$entry.=$_POST["homepage"];
$entry.="'>";
$entry.=$_POST["homepage"];
$entry.="</a>";
$entry.="\n";
$entry.="Comments:  ";
$entry.=$_POST["comments"];
$entry.="\n";
$entry.="\n";
$entry.="\n";
$entry=stripslashes($entry);
fwrite($file,$entry);
fclose($file);
}
}
if ($_POST["post"])
{
if ($_POST["name"]=="")
	 {
	 echo "At least give your name";
	 }}else{
$file=fopen("guestbook.txt", "r");
$size=filesize("guestbook.txt");
$contents=fread($file, $size);
$contents=nl2br($contents);
fclose($file);
}
?>
<form action="guestbook.php" method="POST">
Name::<input type="text" name="name"><br>
Email::<input type="text" name="email"><br>
Homepage::<input type="text" name="homepage" value="http://www."><br>
Comments::<Textarea cols=50 rows=5 name="comments">I am a loser</textarea><br>
<input type="submit" name="post" value="Sign">
<a href="index.php">Back to main</a>
<a href="guestbook.php">View book</a><br><br>
<?$file=fopen("guestbook.txt", "r");
$size=filesize("guestbook.txt");
$contents=fread($file, $size);
$contents=nl2br($contents);
echo "Guestbook is currently $size bytes";?><br><br>
<?echo $contents;?>
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