ok this'll work...
Code:
{capture name=vodterms}
{$product.product|replace:" ":"+"}
{/capture}
Then...
Code:
{include file="buttons/video_on-demand.tpl" style="button" href="http://www.sitenamehere.com/search/super_search.jhtml?action=newSearch&sources=gl&searchTerms=`$smarty.capture.vodterms`"}