Go to the Configuration tab of your VMware vSphere Server, then click on Virtual Machine Startup/Shutdown.
By default (I'm pretty sure) automatic startup is disabled. To enable it, click on "Properties…" on the far upper right of the window.
You'll now see this window:
Check/Tick "Allow virtual machines to start and stop automatically with the system".
Now, this is the bit where I nearly cried…
You know you want to "enable" your Guest OSes to automatically boot, but how? I tried clicking and dragging, right clicking for a context menu to enable "Automatic start up" and gave up.
Turns out, you need to click on the Guest OS you'd like to enable, and then click "Move Up" until it sits underneath the "Automatic startup" title. Argh!
