How can I get from Beijing airport to Grand Mercure central hotel.. thanks

Here are two ways for you:
1. Take shuttle bus line 2 to Xidan Lukou Nan. Then you can easily walk to your hotel.

2. Take Airport Express Train to Dongzhimen, where transfer to local subway line 2 to get off at Xuanwumen Station. Get out from exit B2 and you can easily find your hotel.