I know it doesn't get cold down here in Houston, but I've alway been told to use Stanadyne diesel fuel additive. Here is a link if you want to know more about it.
http://www.stanadyne.com/new/ppt/ppt_dfa.asp It should help with your cold weather starts. I usually put it in about once a month, but have been told by my brother who ones a diesel truck and 18 wheeler to put it in every time I fill up.
Jgar