import vix

server_h = vix.Vix()
server_h.Connect(hostname='hostname',
                 username='username', password='password',
                 provider=vix.Vix.VIX_SERVICEPROVIDER_VMWARE_VI_SERVER)

running_vms = server_h.FindItems()

#vmware-server 2.0 and newer
all_vms = server_h.FindItems(searchType=vix.Vix.VIX_FIND_REGISTERED_VMS)

server_h.Disconnect()