  The top quark and its properties within and beyond the Standard Model will be
extensively studied at the incoming Large Hadron Collider. Nonetheless the top
quark will play the role of the main background for most of the Higgs and new
physics searches. In this paper the top as a background to H=>WW=>2l2nu Higgs
discovery channel will be studied. The current status of the Monte Carlo tools
for t-tbar and single top simulation will be presented. Finally the problem on
how to evaluate the top background from the data will be addressed and the
related systematics will be discussed.
