You will have to look in the yellow pages ("gouden gids") for ballroomdance schools in the neighbourhood. Usually the new year's parties are closed events, but it can't hurt to ask... The bigger danceschools are the place to ask for information: they hold big and open parties, so everyone can visit if they like. I'd say, ask around and see

Unfortunately, I'm not anywhere near Eindhoven/Nijmegen, so I can't recommend you any danceschools to go to I looked in the yellow pages though, and maybe you can try the following danceschools:
Eindhoven: "Friends", "Everybody", "Internationale Dans Eindhoven";
Nijmegen: "Danscentrum Vermeulen", "Danscentrum Henny Brugmans", "Danscentrum Elvira Eggenhuizen", "Wanders Dance Masters"

Good luck! And happy holidays