i wouldnt. they always do that with package deals, throw underpowered amps in with decent subs. the RMS rating is usually half of the peak output rating, so a sub with a 1200W peak would be about 600W RMS(constant power). so a 600W RMS amp would be perfect, but getting anywhere close is good.
it all depends on what your looking for though. if you just want some bump, a package deal from best buy or circuit city will do the trick, especially if they will hook up the install for free, however i would stay away from online package deals. the best way to go is definitly piecing the system together yourself.