Hi,
I am using resolution 800X600
If I try to go little higher It make tile patern.
Like it copy it self again, like replicate it self.
like I start seeing multiple borders and stuff.

Any idea how I can make it to atleast 900X700 or over?

Check the file /etc/X11/xorg.conf

In the section called display, there will be details of what resolutions to use at what bit depths, The mode lines, add resolutions by order of preference, it will try them sequentially until one works.

Modes Modes "900x700" "1024x768" "800x600" "640x480"

I dont see any thing but 800X600

=======================================================================
Section "Monitor"
HorizSync 31-38
Identifier "Monitor[0]"
ModelName "800X600@60HZ"
Option "DPMS"
VendorName "--> VESA"
VertRefresh 50-60
UseModes "Modes[0]"
EndSection


Section "Modes"
Identifier "Modes[0]"
Modeline "800x600" 38.34 800 832 928 1024 600 604 608 624 -HSync -VSync
EndSection


Section "Device"
BoardName "Radeon LY"
BusID "1:0:0"
Driver "radeon"
Identifier "Device[0]"
VendorName "ATI"
EndSection


Section "Screen"
DefaultDepth 24
SubSection "Display"
Depth 15
Modes "800x600"
EndSubSection
SubSection "Display"
Depth 16
Modes "800x600"
EndSubSection
SubSection "Display"
Depth 24
Modes "800x600"
EndSubSection
SubSection "Display"
Depth 32
Modes "800x600"
EndSubSection
SubSection "Display"
Depth 8
Modes "800x600"
EndSubSection
Device "Device[0]"
Identifier "Screen[0]"
Monitor "Monitor[0]"
EndSection


Section "ServerLayout"
Identifier "Layout[all]"
InputDevice "Keyboard[0]" "CoreKeyboard"
InputDevice "Mouse[1]" "CorePointer"
InputDevice "Mouse[3]" "SendCoreEvents"
Screen "Screen[0]"
EndSection

Section "DRI"
Group "video"
Mode 0660
EndSection