^arrey!gautham ur using VESA driver!thats why all this mess!
edit ur /etc/X11/xorg.conf and edit section "device" and in place of "vesa" enter "i810" for old ubuntus and for latest gutsy enter, "intel" save and reboot or open a terminal and do a "sudo telinit 1" and then in runlevel1 press CTRL+D to have the system boots normally!
Also,if ur monitor is not displaying edges correctly,google for ur monitor model and get its Horiz and Ver Freq and manually enter!and if u have a LCD display,u need to enable SUB-PIXEL RENDERING!
if u want to control more,than a casual user in debian or ubuntu,do a "sudo dpkg-reconfigure debconf" and select "medium".now proceed!
also,it is worth to read "newbiedoc" in debian or ubuntu(u can apt-get install newbiedoc
)
open synaptic and make sure u have installed libgl1-mesa-glx ;also,if u have tried to install some graphics driver via compiling from source,mark for reinstallation,libgl1-mesa-dri,libgl1-mesa-glx,mesa-utils,xserver-xorg-video-i810 or xserver-xorg-video-intel depends on ur intel mobo gfx!