I recommend using Ubuntu. They just came out with their new version 7.10. It is a very easy to use OS. Linux has some great features to it, but keep in mind that it is not Windows. It doesn't run Windows software, except through Wine, which doesn't guarantee anything. It doesn't work anything like Windows. You will have to learn new ways of doing things. If you keep those things in mind, you will thoroughly enjoy your experience. If you want to familiarize yourself with Ubuntu, or ask questions about it, go to their forums at Ubuntu Forums
To install it, go to their download page and download the installation CD. This will be in an .iso file format. Windows XP will not natively burn an .iso image to a CD, so you will have to use a 3rd party CD burning software like Nero or the free CDBurnerXP Pro: CDBurnerXP Pro - Reviews and free CDBurnerXP Pro downloads at Download.com
And ps - there is nothing wrong with asking people about which distro is a good one to use. Sometimes hearing people's testimony from experience is better than sifting through a webpage full of specs.
pps - There is a Linux section on these forums that might be a better place to ask those kind of questions.