A suggestion I would make if you want a secure remote desktop would be to use freenx server. It is built in allready in centos. it is very fast and runs securely through ssh port 22. I haven't used VNC in years.
1. install freenx
yum install freenx
2. Now you need to get the key for the client to acess the server. you won't be abl to connect with an nxclient unless you have the client.id_dsa.key
By default the key on centos is located here.
it will look something like this>
-----BEGIN DSA PRIVATE KEY-----
-----END DSA PRIVATE KEY-----
copy the contents of this text file to your client. I am going to assume it is a ms windows client.
To get the contents of this file it is easiest to use a client like WINSCP to get it. http://winscp.net/eng/download.php
in winscp go to this file
and copy it your windows desktop.
3. install free nomachine nxclient for ms windowshttp://www.nomachine.com/download-client-windows.php
4. in the configure button under the Key button you can paste the contents of the client.id_dsa.key we worked with above into this field.
5. logout of your server if you are in there as root & login to your desktop as root with nomachine client.
more info here: http://wiki.centos.org/HowTos/FreeNX