www.theshopperinc.net - classified paper with rentals/homes for sale in towards the back of the paper
www.willistonnd.com - many good links on this site for Williston info. Also check out the RELOCATION GUIDE on the ride side of the home page.
Good luck. Housing is very tough to come by. The only good thing about the snow today is that some people that can't handle the ND winters might be heading back home. That might open up some places for you but there is a huge demand for housing in Williston. Minot would be a better place to look.
Fargo is on the other side of the state from the oilfield. 420 miles from Williston. 7 hours or so.