The easiest thing to stat with is a Linux "live CD" -- a bootable Linux CD which lets you learn, work, and play without modifying your existing PC at all. Knoppix (www.knoppix.org) is the reigning king of these. You'll be able to see the documents on your existing hard disk while you're running Knoppix.
Once you've done some learning, you'll be in a better position to set your system up to dual-boot from the hard drive, and better able to evaluate your many options in this area.
and if you search for and read a few how-to's on creating a dual boot machine, it is fairly simple and trouble free these days. Particularly if XP is installed first, since Linux can just move it to the side.
I find it easiest to install Linux on a separate hard drive. This makes it so you don't have to mess with repartitioning the hard drive that contains Windows and risk losing any data it might have. You can probably scrap a <20GB drive from an older machine which will give you plenty of space to get started. In fact, a 6GB drive will be big enough for most typical installs.
I have been using Linux dual boot machine for a few years now, and especially like the SuSE Linux distribution which is very easy to install even if you have never used linux before. The graphical/text installer can actually resize a Windows NTFS partition and let you use a part of an existings HD, in fact this is what I have on the computer I am sending this posting from.
A few pointers if you are willing to give it a shot: 1. Always back up!!! I remember reading once on a CD box "Don't be a fool back up is cool!" the guy/girl that put that their was very smart and I became so ... . The installation will probably go flawlessly as I have done it numerous times without major problems, but I know nothing about the pc/laptop you plan on using so back up. 2. If you are going to install on the same HD run the Windows disk checking utility and the defrag utility, before the install, to have windows rearrange everything more efficiently before Linux starts slicing its part. 3. If you wish to keep and use both OSes at different times, which in many cases is required (not all programs are available on all OSes). Create an FAT partition so that you can have a place where to store information and use it in any operating systems. NTFS will not be writable in Linux and Windows, of course, cannot even see a standard Linux partition Reiser or ext2/3 etc.
If you wish to try SuSE check out www.opensuse.org if you wish to try something else checkout www.distrowatch.com, you will find CD distros there Knoppix is a really good one e-Live is good looking one . There is a lot of variety in Linux and it all comes down to what you want, but it is a great OS!
Windows, of course, cannot even see a standard Linux partition Reiser or ext2/3 etc.
You can get extensions to the windows explorer to allow it to browse and manipulate ext and reiser file systems (aparently). I had a dual boot xp on ntfs/fedora 4 on a reiser file system but I mangled the fedora filesystem before trying the tools from Windows.
Thanks for the pointer this is news to me and interesting news. I have though given up on having a single drive as my work makes me use many on different OSes so I am "lugging" a USB drive from smartdisk that has an FAT partition and works anywhere I plug it MAC, Linux, Windows. I wish to experiment with an encrypted partition but I like the flexibility.
I saw on the other thread someone mention that FAT is slower than NTFS, I do not thing that is the case as it does not contain security info, which makes it faster to read and manipulate.
I just want to add that if you try a distribution and don't like the result (for example hardware detection wasn't good enough for you), it is a good idea to try another one. Not all the distributions are equal in detecting your hardware or/and in performance after installing them. I prefer the one CD distribution and after that I add what I need. In general every one has its advantages and disadvantages, also depends on your needs and taste. Personally i like the Debian based distributions like: Kanotix http://kanotix.com/ is both live CD and installation CD based on Knopix (this is my favorite one) Mepis http://www.mepis.com/ also live CD and installation one Ubuntu http://www.ubuntulinux.org/ either live CD or installation CD
If you have old PC you might look Vector Linux http://www.vectorlinux.com/ , this one based on Slackware and I read very good reviews about it, didn't try it yet though. And if you want very small linux (50 MB download), you can try http://www.damnsmalllinux.org/ which is both live CD and installation CD.