I'm pretty sure that all that you have to do is simply print / echo $Description variable.
Another thing that you have to do to replace all $Name and similar things in HTML code with their values is to embrace them with PHP marks <? and ?>.
I'm not quite sure whether it will be OK or not, but you may try it out...:
[HTML]
<? $Name ?>
<? $Item_num ?>
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CLOSE WINDOW
[/HTML]
Of course, there is a limitation that surrounding has to be written as php document for this to have any effect, other wise you'll get just printed out variables with <? and ?> as a decoration...