What is the difference between VPS and VDS, and between KVM and VZ?
The main difference between VPS and VDS is the virtualization type. The VPS uses OpenVZ technology, and VDS - KVM. Also, VDS, plans allows installing Windows, FreeBSD.
OpenVZ is the virtualization on OS level. General server core is used by all virtual machines. The main advantages of OpenVZ is a speed of work. The reinstallation of OS is done in a few minutes or you can do a fast reboot of your server.
KVM - is a new technology, that is not a module it is a part of the core. Using KVM you`ll have a full root access to the system and can easily install additional software. KVM allows installing OS for visitors and VNC, that allows running a virtual server like the part of your desktop computer.