Finally I chose a netbook ViewSonic VNB 102p, it is based on Intel N450 Atom platform, the price is reasonable (less than RMB2000). I evaluated several OSes and installed MeeGo and Ubuntu Remix 10.04, these are designed for netbooks. Amazingly, all devices work out of box on these 2 OSes.
When I started to use this new netbook, I found I spent more time on MeeGo than Ubuntu. It might be because everything is fine on Ubuntu but I need some time to make some applications work on Meego. And Meego looks more simple, faster to start. I installed and customized thunderbird (for mail), openoffice 3.2.1 and skype (for voice chat), compiled Shrew (for VPN) and Shotwell 0.6.1 (for managing photos and online albums). Now I have used it for one month and this netbook can meet my demands for daily use.