how to install ubuntu on my pc which have xp installed?

i'm a new in linux

If you have a usb stick of at least 8Gb then try
https://help.ubuntu.com/community/Installation/FromUSBStick

Otherwise try
https://help.ubuntu.com/community/Installation#Installation%20without%20a%20CD

Having made some way of booting into Ubuntu then try this
https://help.ubuntu.com/community/WindowsDualBoot
but where it says things like "boot from the cd" you'll obviously use your way instead ;)

I think the Usb instructions are quite tough to follow because the one page tries to include too many different uses of a Usb stick so good luck using the bits that you need and ignoring the rest.

Good luck and regards from
Tom :)

thx Tom for your replying, i'm traying to burn an image cd from www.ubuntu.org but i hope that the installation will be easy

Here's the best place to get Ubuntu iso from but there are quite a few other places hosting it too :)
http://www.ubuntulinux.org/getubuntu/download

Usually the cheapest 'write once' blank cd's are better than the expensive multi-write ones. I think that once you have made a bootable version the best thing to do is to try booting up with it and when you get to the Ubuntu menu try the top option "Try Ubuntu without any changes to my machine" (something like that) and just seee if that gets you to a working desktop. If it does then we call that a "LiveCd session" (even tho it might not actually be from a Cd) which can be good to play around with. See if it can find your network, see if the internet browser "Firefox" can connect to the internet and check to find "Places" on your Windows partitions. If there are any troubles then come back and ask us how to fix them before you install. Then you should be able to install, and easily fix those problems. Often something that seems quite bad is really easy to fix. Usually there are no troubles but it's good to be prepared and to try out the Live'Cd'

Good luck and regards from
Tom :)