from my understanding, entering game mode should change to the requested resolution if it's supported
problem is, on my system it doesn't, it just locks the screen placing the window in the top left hand corner...
i'm running Debian 5.0 Lenny which uses freeglut 2.4.0
from what i read on google freeglut uses the WM to request resolution change and it may work on some WMs (KWM) and not others (Metacity)
my suggestion is that on linux libxranr is used to do this instead
i don't know if this has been handled with the 2.6.0 release or not but i hope so and if not i hope it can be slated