ESXi 3.5 does ship with the ability to run SSH, but this is disabled by default (and is not supported). If you just need to access the console of ESXi, then you only need to perform steps 1 - 3.
1) At the console of the ESXi host, press ALT-F1 to access the console window.
2) Enter unsupported in the console and then press Enter. You will not see the text you type in.
3) If you typed in unsupported correctly, you will see the Tech Support Mode warning and a password prompt. Enter the password for the root login.
4) You should then see the prompt of ~ #.
Edit the file inetd.conf (enter the command vim /etc/inetd.conf).
5) Find the line that begins with #ssh and remove the #. Then save the file.
6) Once you've closed the vi editor, run the command /sbin/services.sh restart to restart the management services. You'll now be able to connect to the ESXi host with a SSH client.