UPDATE (March 16, 2011):There is no need in this trick starting from the ESXi 4.1. You can configure it.
- got to your VMware ESXi host
- press Alt-F1
- then type “UNSUPPORTED” and press <enter>
- login with your root login and password
- edit the inetd.conf file by typing “vi /etc/inetd.conf“
- remove the comment # in front of the SSH lines
- reboot your ESXi server