Nadolig Llawen:
Na (as in Na t King Cole) dol (as in Doll) ig (as in igloo) [So far, so easy!)
Ll (this is the difficult bit! The initial letter 'Ll' is pronounced by placing the tongue against the roof of the mouth and then exhaling both above and below the tongue whilst bringing the tongue down to its ususal position just touching the back of the lower teeth. Keeping the mouth open throughout) aw (pronounced 'Ow' as in 'that hurts') en (pronounced as in hen or ten).
All together, Nadolig Llawen, a Blwyddyn Newydd Dda (and a happy new year)

Nigel