Replace the object and embed tags for your movie with this,

Code:
<SCRIPT LANGUAGE="JavaScript">

var ip = '<!--#echo var="REMOTE_ADDR"-->';
document.write('<object classid="clsid27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=5,0,0,0" width=550 height=300>');
document.write('<param name=movie value="movie.swf?ip=' + ip + '"> <param name=quality value=high> <param name=bgcolor value=#ffffff> <param name="menu" value="false">');
document.write('<embed src="movie.swf?ip=' + ip + '" quality=high bgcolor=#ffffff menu=false width=550 height=300 type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash"></embed>');
document.write('</object>');
// End -->
</script>
I've never tried finding the users ip address, but if the variable is being created okay, then this should pass it to the movie. Note to change any parameters in these tags to match your movie, eg #version=6,0,0,0 if you used flash mx.