From VMware's Setting Configuration Options on the User's Computer :
Hot Keys for Switching Directly to Virtual Machines and the Host Computer
You can specify a hot key or hot key
combination for switching directly to
any available virtual machine on a
host computer. Each time you press the
specified hot key, the screen display
switches to that of the specified
virtual machine. You may also specify
a hot key for switching directly to
the host operating system.
If any particular virtual machine is
not running, pressing the hot key for
that virtual machine has no effect.
You define the hot key used to switch
to a virtual machine by adding a line
to the target virtual machine's
configuration (.vmx) file. The value
of this option defines the hot key. It
is specified as key,modifier.
There is no default.
For example, to use Ctrl-Shift-F1 to
switch to a particular virtual
machine, add the following line to
that virtual machine's .vmx file, or
modify its value if the option is
already listed.
FullScreenSwitch.directKey = "0x70,0x6"
You define the hot key used to switch
to the host operating system by adding
a line to the global configuration
file (config.ini). The value of this
option defines the hot key. It is
specified as key,modifier. There
is no default.
For example, to use Ctrl-Shift-F9 to
switch to the host operating system,
add the following line to the
config.ini file, or modify its value
if the option is already listed.
FullScreenSwitch.hostDirectKey = "0x78,0x6"