gnome: problem saving screen resolution

[Peter Milne <p.milne@ntlworld.com>]

Using Sarge. Have chosen a higher screen resolution (1024 x 768) in 
Gnome 2.8.3 but Gnome reverts back to 800 x 600 each time I log out. 
Have ticked box to save settings.

gdm appears to run in the higher resolution mode OK

Any advice welcome?