Dewars for Freezing long term? - (Apr/19/2012 )

Hi, I wanna do a small scale experiment on my own but I'm new to this. Could someone tell me if dewars could be used for long term storage or do I need to get some sort of cryo system? What would be the best option for long term storage of just a few vials?

long-term storage either in liquid nitrogen in big specialized tanks or -80°C freezer