You can use the same keyboard shortcuts in a VM as on a physical Mac, but you have to be fast. Start with the VM powered off.
1. Click the power button in the middle of the VM's window to power it on.
2. When the mouse pointer changes to a hand, click inside the VM window a second time. The mouse pointer should vanish. This connects you to the VM keyboard.
3. Press whichever hotkey you want to use: Command+S for single-user, Command+V for verbose, Shift for Safe Mode, hold "C" to force boot from CD/DVD, hold "N" to force network boot, Command+R to boot the recovery HD on Mac OS 10.7+, or hold Option to go to the firmware boot menu.
You have to complete all the steps before the VMware logo is replaced by the Apple logo.
Cheers,
--
Darius