modify pwd:
passwd
add user
useradd user1
passwd user1
groups
groupadd
install GUI (version centos 6.2)
# yum -y groupinstall "Desktop" "Desktop Platform" "X Window System" "Fonts"
http://www.idevelopment.info/data/Unix/Linux/LINUX_AddGNOMEToCentOSMinimalInstall.shtml
startx
# yum -y groupinstall "Desktop" "Desktop Platform" "X Window System" "Fonts"
原文：http://www.cnblogs.com/zyip/p/4208181.html