Caution:.......................
     1.(don't forget)#cp /var/lib/tftpboot/isolinux.cfg  /var/lib/tftpboot/pxelinux.cfg/default


Step:......................
#install tftp-server syslinux dhcpd
#cp /usr/share/syslinux/pxelinux.0  /var/lib/tftpboot/
#vi /etc/dhcpd/dhcpd.conf
          (you should have a right config file of dhcp first)
       Add   filename "pxelinux.0"
             next-server $(your ip);
#mkdir /var/lib/tftpboot/pxelinux.cfg
#cp /var/lib/tftpboot/isolinux.cfg  /var/lib/tftpboot/pxelinux.cfg/default
#chkconfig tftp on
#/etc/init.d/xinetd start