In general, it won't hurt your speakers to run with too little power. By that logic, it'd be bad to play your speakers too quietly no matter what amp you have hooked up to them. The logic behind minimum power rating is probably that the speakers are not that efficient, and you will need to turn the amp up fairly high to get to an acceptable volume level. With a low power amp, the likelyhood that this "acceptable" level is actualy distorting the amps output is fairly high. You're probably better off looking for more efficient speakers designed for the power you're going to be putting into them.

Matthew