Do you have SSH or Telnet access to the Linux machine? (Typically, SSH is more reliable in trouble situations, but either can work.)
Login, use top or, ps, or pgrep to get the process id (pid) of whatever needs killing, and then kill away with kill PID or kill -9 PID on the command line. If you have a new enough system, you can even kill processes from within top by choosing one and pressing 'k'.
Furthermore, ssh and rsh can be used to remotely execute commands without the whole interactive login session, if that's what you end up needing in the future.:
$ ssh USER@HOSTNAME COMMAND