There have been a few occasions where I have wanted to install CentOS on a remote machine that already had a working flavor of Linux on it. Luckily RHEL / CentOS has a way to do this.
- Download the PXE CentOS kernel and initrd image
- Configure the bootloader to boot the CentOS kernel by default
- Configure the bootloader with extra parameters for networking and remote VNC
- Reboot the machine
- Run the vncviewer in listen mode with port 5500 accessible