Hello i`m a newbie with Linux distributions. i want to install ubuntu 11.10 on my computer but keep my win xp (installing from cd - if that matters) so the problem is
that ubuntu can`t detect my xp and see my hard disk empty and suggest to erase it all and then install but i want to keep my info and after that it says "no root file system is defined" and can`t continue my configuration is AMD sempron 2200+ 1,5ghz 512mb of ram 160gb seagate

When you get to the partitioning stage of the Ubuntu installation, there is a manual option. Have you tried that?

i guess i`m to this partitioning stage of the Ubuntu installation but there`s no manual the only option is new partition table and when i click it the system tells me if i proceed with creating a new partition table on the device then all partitions will be removed -i think that this will erase all my data but i want to keep it so there is no way ahead

My best guess is that you have misunderstood the choices during Ubuntu install and it can actually see the xp partitions, and it can see there is currently no room outside the windows partition to install Ubuntu.

First step is you need to have unpartitioned space for installing Ubuntu. Have you done that yet? If not, it is best to do so before using the Ubuntu CD as an installer:

First step of the first step is to boot up xp and use its internal tools to defragment the partition. In some cases, doing that well requires disabling and deleting the paging file, then defragmenting, then later (but not right away) reenabling the paging file.

After defragmenting the windows partition, you should boot the Ubuntu CD in liveCD mode (not install mode) and start up the GUI partitioning tool (I don't recall Ubuntu liveCD details well enough to know which GUI partitioning tool is there or how to start it, but it shouldn't be too hard to find).

At that point, you should see more clearly whether you were correct that Ubuntu can't see the Windows partition, and you would have better tools for looking around to get info to support asking for expert help. More likely, you'll see Ubuntu can see the Windows partition and at that point you would shrink that partition to make room to install Ubuntu.

After shrinking the Windows partition, I would reboot Windows, which tends to force a disk check. If paging was disabled, I would reenable it. Then make sure Windows is still healthy.

THEN you are ready to start the Ubuntu install, which should make more sense now that there is a place for it to install.

If you have the standard Ubuntu 11.10 CD, you should have two options when you boot. One is to Try Ubuntu and the other is install. Click the Try Ubuntu option as suggested above and you should then get to a Desktop with an install Ubuntu icon. After clicking that and you will see a Welcome screen where you select a language, click Continue and you will get the Preparing to Install Ubuntu screen which shows options for best results while installing. After clicking Continue on that page, you will get to a new page which should show several options. The one you want is Something Else. Select the radio button, click Continue and you should see a new window showing any drives/partitions on the computer.

You need to click on free space then click on the Create tab. If you don't have free space you need to create some or you need to select a partition to overwrite and then click the Edit tab. The "no root file system is defined" means you didn't select a mount point when you were creating your partition.

You might try booting to the Desktop, openeing a terminal (hold down the Ctrl+Alt+t keys) and getting partition info to post with this command:

sudo fdisk -l (lower case Letter L in the command)

It's pretty hard to be any more detailed as we don't know your partition information. More details on the steps you have taken would also be helpful.

my partitions are c:-windows d:-empty formatted e:-music movies and so on.
i`m starting the ubuntu live cd starting gparted and there shows me that i have 149,05 gib unallocated
in the terminal after typing sudo fdisk - l it gave this response fdisk:unable to seek on /dev/sda/: Invalid argument.
as for the steps i`m taking i write the cd from ubuntu.com after booting from it either i choose install or first try and then install on the first choice for language i choose English then for the preparing to install marking the two options (download updates while installing and install third-party software) and click continue the next screen that appears is installation type and then is written this computer has no detected operation systems.What would you like to do?
erase disk and istall Ubuntu
something else - is what i choose
and after this screen the next is а table with columns |device|type|mount point|format?|size|used
under this is written /dev/sda at the bottom options only new partition table is available and at the bottom of the screen it`s a dropdown menu with only one option -/dev/sda/ ATA ST3160815A (160.0 GB) and if i choose install -no root file system is defined.

Ubuntu has problems to read your partition table and therefore wants to write a new one during install. This is most likely caused by a disk that is not partitioned in the conventional way but uses Windows' dynamic volumes. Those dynamic volumes are currently not supported by Linux, so your only chance to install Ubuntu (which by the way I would not recommend on a machine with 512MB RAM) is to backup your data to an external device, re-partition the disk in the conventional way and then install XP and Ubuntu.

10x anybody for the help i erase everything on the hard disk and install ubuntu (finally) as written it didn`t go very well on 512ram i`ll try debian