My laptop is Dell Inspiron 1505, with ATI Mobility Card

When i installed Ubuntu Feisty X-Server was not starting. Instructions to fix:
sudo apt-get update
sudo apt-get install linux-restricted-modules-$(uname -r)
sudo apt-get install xorg-driver-fglrx
sudo depmod -a

After that reconfigure X Server

sudo dpkg-reconfigure xserver-xorg

Select fglx driver, keep remaining all default settings(for keyboard etc). Do not auto detect monitor (this hangs on my system)

After you done with reconfiguring restart your xserver or just reboot your machine.

To fix resolution problem:

Fix Resolution

It took me a while to fix my resolution. I wanted 1280×800@ 60 resolution for my dell laptop. After lot of googling i got some help.

1. sudoedit /etc/X11/xorg.conf. Make following changes:

Section “Monitor”
Identifier “Generic Monitor”
Option “DPMS”
HorizSync 28-64
VertRefresh 43-60
Modeline “1280×800@60″ 83.91 1280 1312 1624 1656 800 816 824 841
EndSection

Do determine for modline for your resolution: modline calci. Accordingly you add Modline.

Next in Screen Section keep only resolution that you want.
Section “Screen”
Identifier “Default Screen”
Device “Generic Video Card”
Monitor “Generic Monitor”
DefaultDepth 24
………
………

SubSection “Display”
Depth 24
Modes “1280×800″
EndSubSection
EndSection

After this changes restart X server. Then System >> Preferences >> Screen Resolution and select your resolution.

Hope this will help !!!!

Few useful links
ben robinson’s blog