I will have to agree with Art Vandelay that a DOT certification doesn't tell much of the story. The skullcap he links to is DOT certified, but I would never wear it and I don't think it's very safe.
Every motorcycle helmet sold in the US is DOT certified, but it requires no testing on the manufacturer's part. SNELL or ECE will give you a better picture of how safe the helmet is. Your best bet as everyone here is suggesting is to research the helmet and stick with a reputable company.
http://www.ninjette.org/forums/showt...ell#post366698