Block Snippet, Clean URL, file_exists() function problem

My task..

was to switch a block's content image/swf in particular pages. Usually the pages could be a node or taxonomy term. So i had written a block snippets to check for image/swf file's existence using file_exists where i have saved such images in a particular logic. What i was trying to do, is to get the node id and look for an image or swf in files folder.

Now about the problem, i was using Clean URL in my drupal 5.7 installation. The following code did not worked when the Clean URL is activated. But worked fine when Clean URL was disabled. by debugging ( echo :( ) i saw that when clean url was activated file_exists() always returned false.

Though clean URL or query URL is not a major issue in my required work. But i prefer Clean URL. So, can anyone refer the actual cause of the problem or where am i wrong??

Thanks in advance.

<?php

  $image_path = base_path() . "files/images/";
  $dflt_image = "top_image_1.jpg";
  $image_prfx = "top_image_";
  $swf_prfx = "top_swf_";
  
  
  $id = 1;
  if( arg(0) == 'node' and (int)arg(1) != 0 ) 
		$id = arg(1); /* Getting Node Information */	
  
   
  // Looking for image
  if( file_exists($image_path . $image_prfx . "$id.jpg") and $id != 1) {
	echo "<img src='" . $image_path . $image_prfx . "$id.jpg' />";
  }  
  else if( file_exists($image_path . $swf_prfx . "$id.swf") ) {
	// Looking for swf
	echo '
	 <object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" 	
				codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,29,0" 				width="970" height="200">							
			<param name="movie" value="';
	echo $image_path . $swf_prfx . "$id.swf"; 
	echo '" />
			<param name="quality" value="high" />							
			<param name="play" value="true" />							
			<param name="loop" value="true" />							
			<embed src="';
	echo $image_path . $swf_prfx . "$id.swf"; 
	echo '"  								
			quality="high" width="970"								
			height="200" name="movie" align="" 									
			type="application/x-shockwave-flash"								
			plug inspage="http://www.macromedia.com/go/getflashplayer"> 							
			</object>';
			
  }else {
	echo "<img src='" . $image_path . $image_prfx . "1.jpg' />";
  }
?>