You need to edit your
/etc/X11/xorg.conf configuration file. In the file there is a device section for your graphics card, where the driver is defined. It may have been reverted to
vesa driver (which only supports 800x600 I think), if the nVidia driver does not work. You could try
nv driver instead, if I remember right then 'nv' is the open source nVidia driver which should work with your card, though it doesn't provide you with too good direct rendering capabilities.
There are some configuration programs/scripts for X too, but they depend a bit on your distribution. In the X config file I mentioned above, are defined all the resolutions available (first in the list is the one that is used if it works, if not then second, if that doesn't work either then third, ...), colour depths (note: there are resolutions list per each depth), graphics card (device) and the driver to use with it etc..there are also font paths, keyboards and other input devices. For more information about it, run this:
Since Fedora uses Xorg, and not XFree86, that should be for you. That might be a bit difficult to understand at first (but the file is really simple after you get used to that; altering it directly is easy), but luckily there is a lot of good documentation on the web about configuring it, along with configuring it for nVidia drivers etc..
