ummmmm
if they can travel in space several hundred thousand AU's (Astronomical Units(the distance between the earth and the sun)) and sustain there life for that long to travel here, I'm pretty sure they have better technology then us. sure we can nuke them sure we can throw all we gut but honestly you think we are anything compared to a species that can travel LIGHTYEARS and great distances in space for long periods of time. sure we can go to the moon. We have scanned half our galaxy for a earth like planet and found 2. one on the other side of the galaxy and the next closest is 8.5x10^6000 AUs away.
they will kick our buts but unless they are hippie planet lovers that live primaly like the Na'vi then we are screwed.