1. It snowed twice in Beijing recently, and it is very cold.
2. The tourist sites will not be closed.
3. No, tourists can visit and climb the Great Wall. But remember to keep warm; it is much colder on the Great Wall.
4. Sweater, down garment, gloves, scarf and hat are recommended.

I just came back from Beijing on 15 Nov 2009,
1) fluctuate around 0`C,
2) attractions in city will not be closed. We actually wanted to visit Mutianyu Greatwall, but the road was blocked due to heavy snow. We went to Juyongguan instead.
3)Is quite slippery after snow. You need a pair of hiking shoe, and water resistant at least if not waterproof.
4)Wind breaker, Sweater, gloves, scarf, hat and thermal underwear (for the first 2 days if you are going from Malaysia, until you get use to the weather there)
You may want to visit my blog at http://myculturaltrip.blogspot.com