You need:
same shared storage access
sname network for VM
same network of heartbeat (usually the service console/management interface)
VMware HA license
vCenter Agent license
available vCenter Server "connection"... ok if you have vCenter Standard... warning on vCenter Foundation (max 3 hosts)
Andre
Andrew | http://about.me/amauro | http://vinfrastructure.it/ | @Andrea_Mauro