I've been using virt-manager on my Fedora laptop to connect to a headless CentOS 5.X server running KVM (libvirt). virt-manager can remotely connect to other computers that are running KVM.
Look under the File pull-down in virt-manager, where it says "add connection". Check the box that says "Connect to remote host". There are several choices as far as protocols go for connecting to a remote system. In my version of virt-manager (0..8.7) I have the following:
- TCP (SASL, Kerberos, ...)
- SSL/TLS with certificates
The easiest to get going is SSH, IMO. Details on how to do it are covered here: http://virt-manager.org/page/RemoteSSH.
Ultimately virt-manager is doing the following behind the scenes:
virt-viewer -c qemu+ssh://email@example.com/system myvm1
Where 192.168.1.1 is my KVM headless server and myvm1 is one of my guest KVM instances. Alternatively you can remotely run virt-manager from the headless system and tunnel it through ssh with a command like this:
ssh -X firstname.lastname@example.org virt-manager
This works OK too, but I generally only use this in LAN situations, not WAN.