cd /boot

debian 6

wget http://ftp.us.debian.org/debian/dists/squeeze/main/installer-amd64/current/images/netboot/debian-installer/amd64/initrd.gz
wget http://ftp.us.debian.org/debian/dists/squeeze/main/installer-amd64/current/images/netboot/debian-installer/amd64/linux

 debian 7

wget http://ftp.us.debian.org/debian/dists/wheezy/main/installer-amd64/current/images/netboot/debian-installer/amd64/initrd.gz
wget http://ftp.us.debian.org/debian/dists/wheezy/main/installer-amd64/current/images/netboot/debian-installer/amd64/linux

vi /boot/grub/menu.lst

title Install OS
kernel (hd0,0)/boot/linux
initrd (hd0,0)/boot/initrd.gz
boot

保存退出

重启
选择Install OS，进入安装界面.