File Upload With Renaming Using PHP

<form method="post" enctype="multipart/form-data" action="uploadit.php">
<input type="text" name="name1" id="name1">
<input type="hidden" name="action" value="upload">
Upload image:
<input type="file" name="picThumbnail"><br />
<input type="submit" value="upload">
</form>

<?php
	if ($_FILES['picThumbnail']['name'] != "")
	{
		$sUploadDir = 'upload/';
		$sUploadedFile = $sUploadDir . basename($_FILES['picThumbnail']['name']);
		if (move_uploaded_file($_FILES['picThumbnail']['tmp_name'], $sUploadedFile))
		{
		$sThumbnail = $_FILES['picThumbnail']['name'];
					$sThumbnail = $name1."_".$sThumbnail;
					$sFileName = strtolower(($sThumbnail));
					if (file_exists(($sUploadDir.$_FILES['picThumbnail']['name'])))
						rename(($sUploadDir.$_FILES['picThumbnail']['name']), ($sUploadDir.$sFileName));
		echo "file uploaded successfully";
		}
	}
?>