If I read it right, you are looking for a file uploader, so people can create designs for cars then send them in to you by PHP.
The upload script below is the one that firepages wrote, It is the one that I use if I ever need to be able to upload files. Thanks firepages
<form action="upload.php" enctype="multipart/form-data" method="post">
$dir="users"; // Directory name to upload files to
$ext = substr ($myfile, -4); // Strip all but the file extension
$filetypes = array ('.gif','.jpg','.jpe','.bmp','.png'); // File entensions to accept
copy ($myfile,"$dir/$filename") or die("Unable to upload file"); // Upload file
echo "<p style=\"color:green;\">File uploaded sucessfully</p>"; // On Success
echo "<p style=\"color:red;\">Choose a file</p>"; // Text to display before upload
<input type="file" name="myfile"><br><br>
<input type="submit" value="Upload">
Bear in mind that you will have to have the access on your server to be able to upload files. Hope this helps...