ALT + F1 , then type ‘unsupported’. Give ESXi root password and off you go. Full article here:
http://www.virtualizationadmin.com/articles-tutorials/vmware-esx-articles/general/how-to-access-the-vmware-esxi-hidden-console.html
Good video on administering ESX from service console:
http://www.ditii.com/2010/02/25/10-basics-of-linux-to-manage-vmware-esx-through-service-console-webcast/
