Hi,
I have installed Fedora Core 6 in a IBM Thinkcentre (PIV) machine with Intel 845G/GL Integrated Graphics Device. It is supporting only low resolution with 16 bit but not supporting 1024x768 with 24 bit. Can anybody help me ?

What do you mean by 'low resolution with 16bit' ?? What mode is it currently displaying (like is it 800x600 or what?), and what mode do you WANT do be displayed?
I would think that 1024x768x24 would be able to display fairly easily. What video driver are you using? I think it's the i810 driver you would use for that device (don't quote me-- I think it is though).

You should check the file /etc/X11/xorg.conf and make sure that:

A) the correct driver is being used
B) the resolution(s) you would like to use are included in the 'Screen' section
C) The 'Monitor' section is properly configured for the display in your laptop, specifically horizScan, and vertRefresh rates..

I am having the same problem on my IBM NetVista desktop with integrated Intel 845G graphics.

By default, the driver is "vesa", I tried changing this to "intel" and "i810" and neither of those worked, I got just a black screen. Even under "vesa" the only resolution it would display is 640x480x16. Changing the DefaultDepth to anything else, I got just a black screen.

This is with Slackware 12.1.