Windows 2000 allows local users to cause a denial of service and possibly gain privileges by setting a hardware breakpoint that is handled using global debug registers, which could cause other processes to terminate due to an exception, and allow hijacking of resources such as named pipes.
http://www.iss.net/security_center/static/6590.php
http://archives.neohapsis.com/archives/bugtraq/2001-05/0232.html