Need Fix Resolution

I am completely new in Linux...After Install Ubuntu 9.04 X64 ..The computer runs very fine but I still have problem with resolution as the max resolution is 800*600 and I need to run it 1024*768 also the computer hang when I try to run some screensaver.Although My mulimedia video/sound runs perfect ....I made update but no fix done...

I will be so thankful If you help fix this bug.

With Concerning

>>>>My hardware......

• AMD Sempron 3000+ 1.08 GH On Motherboard Via EGC K8M800-M2..
• 512 MB of RAM..
• VGA 64 MB S3g Unichrome Pro IGP >> Built-in....

With this hardware I could ran XP-VISTA very fine before so I need help to get me the best distrbo for me.....

My Xorg.conf says......

# xorg.conf (X.Org X Window System server configuration file)
#
# This file was generated by dexconf, the Debian X Configuration tool, using
# values from the debconf database.
#
# Edit this file with caution, and see the xorg.conf manual page.
# (Type "man xorg.conf" at the shell prompt.)
#
# This file is automatically updated on xserver-xorg package upgrades *only*
# if it has not been modified since the last upgrade of the xserver-xorg
# package.
#
# Note that some configuration settings that could be done previously
# in this file, now are automatically configured by the server and settings
# here are ignored.
#
# If you have edited this file but would like it to be automatically updated
# again, run the following command:
#   sudo dpkg-reconfigure -phigh xserver-xorg

Section "Device"
	Identifier	"Configured Video Device"
EndSection

Section "Monitor"
	Identifier	"Configured Monitor"
EndSection

Section "Screen"
	Identifier	"Default Screen"
	Monitor		"Configured Monitor"
	Device		"Configured Video Device"
EndSection