There are a number of adjectives which come to mind to describe the kind of people who kill themselves in order to kill others - deranged, cruel, evil, vicious, sick, scum - but what they most emphatically are not is cowards. Anyone who is prepared to die to accomplish his purpose, no matter how twisted and malevolent that purpose may be, is not a coward. Why President Bush insists upon calling them that, most recently in his remarks on Benazir Bhutto's murder, is beyond me.
Perhaps he's just taunting the terrorists, but if so, it would make more sense to use some other pejorative. There are plenty of them available which would accurately describe these vermin without having to use one that doesn't describe them at all.
RLC