Haven't used CentOS since the 4.x days, but a quick Google for "VNC CentOS 6" found this, which seems plausible:
http://wiki.centos.org/HowTos/VNC-Server
Also, remember that you'll need to install some sort of desktop environment Otherwise, you'll just get a dithered grey screen with a big × cursor and maybe --
maybe -- an xterm. Among the "Big Three" (GNOME, KDE, and XFCE), I'd recommend XFCE. There's one XFCE machine here at the ranch, and it looks like it would comfortably fit in 512 MB. My freshly-rebooted netbook with gnome+metacity would not.
(Note: it's my wife's computer, and she closed all applications/browsers before heading out of town for the weekend... all bets are off once you start Chrome. She also didn't apt-get upgrade... or empty the dishwasher, or*CLANG* --- where the heck did that frying pan come from)
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