Could have been the boots or the bindings, although I would probably think it's the boots and also the fact that snowboarding will hurt your feet anyways if your brand new at it. Were the boots tightened all the way on the shoe part? If your toes just touched the ends of the boot,(like their supposed to) the boot should have been tight on the rest of your foot. If it wasn't, the boot isn't the right fit for your foot, and like you said is probably a POS anyways.
More times then not it's the boots and not the bindings, because the bindings should ratchet just enough so that your foot is locked, but the straps aren't digging into the boot. You were probably tightening the bindings too tight in order to combat the looseness of the boots.
PowderHound and TreeNinja