for invision board 1.3, u need to be an admin and go to skins->board wrapper->edit. then insert this code anywhere after <% BOARD HEADER %>. Make sure the swf file is in the root directy of your forum.
Code:
<center>
<!-- URL's used in the movie-->
<!-- text used in the movie-->
<!--Guild Wars Release YEARMONDAYHOURMINSECguildkarma.com--><OBJECT classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000"
codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,0,0"
WIDTH="257" HEIGHT="70" id="countdown+clock" ALIGN="">
<PARAM NAME=movie VALUE="countdown+clock.swf"> <PARAM NAME=loop VALUE=false> <PARAM NAME=menu VALUE=false> <PARAM NAME=quality VALUE=high> <PARAM NAME=bgcolor VALUE=#666666> <EMBED src="countdown+clock.swf" loop=false menu=false quality=high bgcolor=#666666 WIDTH="257" HEIGHT="70" NAME="countdown+clock" ALIGN=""
TYPE="application/x-shockwave-flash" PLUGINSPAGE="http://www.macromedia.com/go/getflashplayer"></EMBED>
</OBJECT></center>
And it says 5 days left on mine. perhaps the numbers are a bit small, but i wanted to not be so intrusive to my guildmates.