You can't launch it from the editor but you can run it before or after you start DB. Just make a shortcut and place it on your desktop, start menu, or quick launch.
You can alt-tab to switch between them, run db in a window so they overlap, or do what I do and run dual monitors. I have DB in on one and the help on the other.
Windows tip:
One thing that I do is to tear off my quick launch toolbar from the bottom and run it across the top of the window. I check "always on top" and "auto hide". This makes the quick launch appear by moving the mouse up just a little ways above the normal application menus. My help file is just above and a little to the left of the DBPro help.
Bruce