As long as you have a driver that gets you into X (3d hardware acceration is another thing), then its a matter of getting the right settings in your /etc/X11/XF86Config file. In the "Screens" section, there will be a subsection for each display depth, in those subsections you will find "Modes", this is the order of the resolutions that X (the gui server) will try to display--in the subsection example below the "1280x1024" will try to load up first then "1024x768" and so on...
Modes "1280x1024" "1024x768" "800x600" "640x480"
So for you, you will want to make sure that "1024x768" is the first on the list.
Oh and by the way the driver that comes with slack for nvidia (the nv driver) is OK for 2d but you will want to go to nvidia's site and use their driver for 3d