Same problem.  I took some of the settings from my FC6 xorg.conf and added them to conf in F7.  Here are the changes I made to /etc/X11/xorg.conf to get things working (don't forget to back yours up before editing):
Added this section:
	Code:
	Section "Monitor"
        Identifier   "Monitor0"
        ModelName    "LCD Panel 1280x800"
 ### Comment all HorizSync and VertSync values to use DDC:
        HorizSync    31.5 - 90.0
        VertRefresh  59.9 - 60.1
        Option      "dpms"
EndSection
 Added this line to the Screen section block:
Added this line to the Display subsection:
	Code:
	                Modes    "1280x800" "1152x864" "1024x768" "800x600" "640x480"
 So there's no confusion, here's my entire working xorg.conf:
	Code:
	# Xorg configuration created by pyxf86config
Section "ServerLayout"
	Identifier     "Default Layout"
	Screen      0  "Screen0" 0 0
	InputDevice    "Keyboard0" "CoreKeyboard"
EndSection
Section "InputDevice"
	Identifier  "Keyboard0"
	Driver      "kbd"
	Option	    "XkbModel" "pc105"
	Option	    "XkbLayout" "us"
EndSection
Section "Monitor"
	Identifier   "Monitor0"
	ModelName    "LCD Panel 1280x800"
 ### Comment all HorizSync and VertSync values to use DDC:
	HorizSync    31.5 - 90.0
	VertRefresh  59.9 - 60.1
	Option	    "dpms"
EndSection
Section "Device"
	Identifier  "Videocard0"
	Driver      "vesa"
EndSection
Section "Screen"
	Identifier "Screen0"
	Device     "Videocard0"
	Monitor    "Monitor0"
	DefaultDepth     24
	SubSection "Display"
		Viewport   0 0
		Depth     24
		Modes    "1280x800" "1152x864" "1024x768" "800x600" "640x480"
	EndSubSection
EndSection
 Good luck!
--rick