VNC and KVM are totally different things. For KVM to work you will need Java on the client machine or on the system from which you are accessing the IPMI KVM.

System can be accessed by using VNC client and VNC server, but it will not offer the same functionality and features as IPMI. Also there are serious security issues with using VNC that can allow third parties to gain access to your machine. Please see the VNC documentation on the web.