If you're on a DOCSIS system, no.
A small configuration file is sent to your modem from your provider. This file is what sets your caps and limits. It can not be changed.
Jan 2009 Update: Reports are that there are kits now available to permit this, however the legitimacy of the use of these kits is probably doubtful and you could potentially be penalized by your provider for uncapping the modem. [2kmaro]
Also see »Cable Users FAQ »What if I uncap?