That is for X preferences. His problem is during bootup. I believe the
solution is to edit /etc/default/grub (with administrator's privilege) and
update-grub. To be more precise:
1) Open a terminal (it is in the accessories sub-menu);
2) Type and execute (by pressing [Enter]) the following command:
$ gksu gedit /etc/default/grub
3) After entering your password, uncomment the line #GRUB_GFXMODE=640x480 by
removing the leading # and change 640x480 with 800x600;
4) Add the following line (wherever you want):
GRUB_GFXPAYLOAD=800x600;
5) Save and exit the text editor;
6) Back in the terminal, execute the following command:
$ gksu update-grub;
7) Reboot and tell us, in response to this post, if it has worked. :-)
