In AutoCAD 2008 we added the ability to switch Tool Palettes and Groups at the AutoCAD command line with the command TPNAVIGATE. This means you can now use this in a LISP or in your menu to change the current Tool Palette.

From the AutoCAD 2008 Help

Command entry: TPNAVIGATE

Specify tool palette to display or [palette Group]: Enter a tool palette name, or enter g

• Tool Palette Name
  Displays the specified tool palette.
  Specifying a tool palette that is not part of the current group, displays the specified palette and its palette group.
• Palette Group
  Displays the following prompt.
  Specify palette group to display: Enter the name of a valid tool palette group.
  
  Displays the specified tool palette group. The initial prompt repeats so you can specify a tool palette name.

Note TPNAVIGATE opens the Tool Palettes window if closed.

Cheers,
Shaan