Fileupload on MAC-Browsers won't work

Hi, 
 
The following script works on any browser on windows xp. But not on a
mac (osx)
It simply shows the temp-directoryname.
Is anybody out there who could help me to fix this problem?
How will the upload work with Safari?

Thanks for your help. 
 
This is the form for the upload:  
 
<form enctype="multipart/form-data" method="POST" name="NAForm"
action="IA.php?<?=SID?>">  
<input type="file" name="BildDatei" maxlength="128" size="36" value="<?
echo $Bild; ?>">  
<input type="hidden" name="MAX_FILE_SIZE" value="20480">  
 
 
 
The following site checks the uplad and copies the file to a specific
folder:  
 
// if the Picture was uploaded  
if ($BildDatei!="" AND  
is_uploaded_file($_FILES['BildDatei']['tmp_name'])) {  
// Check for JPG  
if ($_FILES['BildDatei']['type']=='image/pjpeg') {  
// Move File  
$TestFile=$UserCoverDir.$ISBNFeld.".jpg";  
move_uploaded_file($_FILES['BildDatei']['tmp_name'], "$TestFile");  
}  
} else {  
echo "Save unsuccesfull";  
}