i would just stick with 2x500gb hard drives, that way if later on one blows, your not out a whole hard drive
1 500gb is large enough for me, i couldnt emagin filling it, never mind 1tb, i guess if you rip alot of dvds or create alot of iso files you would need the space
if you dont need the extra 500gb, return it or sell it, no need to have more then you need, buy something that is usefull, but if you have the money, go nuts!, lol