my PC has 256MB RAM. May I install ubuntu 8.0.1 ? but it giving me a error during installtion that 256 MB memory are required. How can I resolve the problem ?

You probably do not have 256 Mb, Xubuntu 8.10 is better option to Ubuntu, for you hardware. Can download a .iso on this site:

http://www.xubuntu.org

If you like Ubuntu, use the Alternate Installation Disk, but is considerably more difficult that Live CD.

The other point to consider with your memory (256MB) is that if you have an onboard graphics processor, a part of your system memory will be alotted to the onboard video for its exclusive use, which may be why Ubuntu is giving you this error.
The amount of system memory given to the onboard video can usually be adjusted in your bios options, but as 4MB is most likely the minimum amount, you will either need to upgrade your system memory, install an expansion video card, or follow jacobS advice.

hope this helps clarify a bit.

Cybox.

256MB is fine for Xubuntu. However you will have better chances of success installing from the alternate version of the installer, which is text-based but just as easy to go about.

You can download the PC (Intel x86) alternate install CD from here:
http://releases.ubuntu.com/intrepid/

The file is:
http://releases.ubuntu.com/intrepid/ubuntu-8.10-alternate-i386.iso

Once you boot from it, you will be presented with several options. Choose English for the language, then press F4 to choose "install a command line system" and then "Install Ubuntu" from the main menu. Then proceed as usual, a few questions will be asked.

When the install is complete, you will end up with a base install, without graphic environment. At the text prompt login as usual, then make sure you have INternet access:

sudo dhclient

(password asked is the same as your main user)

Once you have Internet access, update & upgrade:

sudo apt-get update
sudo apt-get upgrade

Then install the Xubunu environment:
sudo apt-get install xubuntu-desktop

This will take a while, then you can reboot:

sudo reboot

And you should be greeted with the standard Xubuntu login.

256 MB will let you run Xubuntu confortably, however you may not get a very responsive system if you try running a lot of applications at the same time. I'd suggest installing the flashblock extension for Firefox if you use Flash, as opening many browser windows with flash applets without controlling them will quickly eat up resources.

Hope this helps understand installation for low-resource systems.