Change the contens of your /etc/apt/sources.list file to the fllowing :
deb http://ubuntu.cn99.com/ubuntu/ dapper main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ dapper-security main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ dapper-updates main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ dapper-proposed main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ dapper-backports main restricted universe multiverse
deb-src http://ubuntu.cn99.com/ubuntu/ dapper main restricted universe multiverse
deb-src http://ubuntu.cn99.com/ubuntu/ dapper-security main restricted universe multiverse
deb-src http://ubuntu.cn99.com/ubuntu/ dapper-updates main restricted universe multiverse
deb-src http://ubuntu.cn99.com/ubuntu/ dapper-proposed main restricted universe multiverse
deb-src http://ubuntu.cn99.com/ubuntu/ dapper-backports main restricted universe multiverse
If you are using China Net,this will let you have a faster downloading speed with apt.
