Most of this information has been obtained by searching on net. However, the information
has to be hunted. This is for using 1366x768 (wide screen) resolution on Fedora 5.

After startx, a file /var/log/Xorg.0.log is created. Use your favourite editor (say vim)
to search for "Supported" (part of file is as follows)

(II) I810(0): Supported VESA Video Modes:
(II) I810(0): 720x400@70Hz
(II) I810(0): 640x480@60Hz
(II) I810(0): 640x480@67Hz
(II) I810(0): 640x480@72Hz
(II) I810(0): 640x480@75Hz
(II) I810(0): 800x600@56Hz
(II) I810(0): 800x600@60Hz
(II) I810(0): 800x600@72Hz
(II) I810(0): 800x600@75Hz
(II) I810(0): 832x624@75Hz
(II) I810(0): 1024x768@60Hz
(II) I810(0): 1024x768@70Hz
(II) I810(0): 1024x768@75Hz
(II) I810(0): 1280x1024@75Hz
(II) I810(0): 1152x870@75Hz
(II) I810(0): Manufacturer's mask: 0
(II) I810(0): Supported Future Video Modes:
(II) I810(0): #0: hsize: 1152  vsize 864  refresh: 75  vid: 20337
(II) I810(0): #1: hsize: 1280  vsize 720  refresh: 75  vid: 53121
(II) I810(0): Supported additional Video Mode:
(II) I810(0): clock: 85.5 MHz   Image Size:  413 x 234 mm
(II) I810(0): h_active: 1366  h_sync: 1436  h_sync_end 1579 h_blank_end 1792 h_border: 0
(II) I810(0): v_active: 768  v_sync: 771  v_sync_end 774 v_blanking: 798 v_border: 0

Edit /etc/X11/xorg.conf (after saving previous version) to add following line (in red):

Section "Monitor"

  ### Comment all HorizSync and VertSync values to use DDC:
  ### Comment all HorizSync and VertSync values to use DDC:
     Identifier   "Monitor0"
     VendorName   "Monitor Vendor"
     ModelName    "WideScreen"
     DisplaySize  410    230
  ### Comment all HorizSync and VertSync values to use DDC:
     HorizSync    30.0 - 83.0
     VertRefresh  56.0 - 76.0
     ModeLine     "1366x768" 85.5 1366 1436 1579 1792 768 771 774 798
     Option        "dpms"

And also add "1366x768" (in blue):
Section "Screen"
     Identifier "Screen0"
     Device     "Videocard0"
     Monitor    "Monitor0"
     DefaultDepth     24
     SubSection "Display"
         Viewport   0 0
         Depth     16
         Modes    "800x600" "640x480"
     SubSection "Display"
         Viewport   0 0
         Depth     24
         Modes    "1366x768" "1024x768" "800x600" "640x480"

Start X one again. If you do not get desired display, then look in /var/log/Xorg.0.log
and search for 1366x768. You may find a line like:

(II) I810(0): Not using mode "1366x768" (no mode of this name)

Search rpm repositories for "915resolution" (maybe old versions are here.)
Install RPM as usual--- using "rpm -i 915resolution*.rpm" (as root) and follow the directions of README there
(As root display the available resolutions :
        # 915resolution -l
Overwrite mode (say 38) as
        #915resolution 38 1366 768 24)

Starting X once again should give the desired resolution. If yes, append (add) the line:
     915resolution 38 1366 768 24
at the end of file "/etc/rc.local"