Im travelling to Beijing on New Years' ( Jan 20- 24, 2012), are the top attractions open?

Yes, they are open all year round.

If you are first time come here,you should visit the scenic spots of Beijing as follows:
1.The Tian'an men square
2.The forbidden city
3.The Temple of Heaven
4.The Ming Tombs--often for Dingling
5.The Summer palace
6.The Great Wall
7.Visit Beijing Hutong by tricycle.
If you are interest in Cultural art of China,you also could watch Peking Opera and The performs of Chinese Kufu and so on.
If there is not snow,you could go visit all the scenic spots during you are in Beijing.You couldn't go to Great Wall and Ming Tomb if snows.