Trousers as in snow pants? Or trousers as in casual wear?
At a minimum you need some type of base layer (think longjohns), and a snowproof jacket and pants. Pants should be rated at 10k for a beginner, and jacket is fine at 5k. The 10k and 5k I mention are waterproof ratings check the sticky thread for more info on this subject. Boots, beanie, goggle, gloves as well. I don't know the weather at where you are going, if you give some details we can help with more recommendations.