Well, unless you want to kill your party before it starts, do NOT play them the Wigan's Ovation version of Skiing In The Snow - it's like playing a version of All Right Now by Westlife! You need the original by The Invitations.
My advice is to pop along to your local library and get some Northern compilations out, there are loads and loads of them - and failing that, if you Google 'Northern Soul' you find masses of titles, then go to UTube and download them off there.