@ Adeli: I\'d say Redhat is a good start, though SuSE will probably be OK as well. You might also try out Knoppix, as it completely runs off a CD, no install required.
However, if you actually want to learn Linux, you need to dig below the pretty graphical UIs (KDE or Gnome), and learn the real power that is the command line. For that, you\'ll need some sort of tutorial or list of commands, which I can\'t help you with. For starters, here are some commands:
cat: the equivalent of type in DOS
ls: the equivalent of dir in DOS
cd: just as cd in DOS, just needs a blank if you type cd.. (Edit: it becomes \"cd ..\" in Linux)
\"/\": the directory delimiter, the equivalent of \"\\\" in DOS (cd / instead of cd \\ for the root directory)
as for an editor, you can use
emacs
nano
pico
vi (totally non-intuitive!)
and there probably are others.
If you want to have something like \"dir /s\", use \"find\". If you need to do some \"/p\" (like in \"dir /s /p)\", use \"find | more\" or \"find | less\" (which allows scrolling).
Also, the man command is your friend (man ls, for example) brings up a description of the program (if available).
the \"Administrator\" is called \"root\" in Linux.
Edit 2: Note that in Linux everything is highly user-based, i.e., you start out with a home directory for each user, and it has a working permision system, things that have been added to Windoze only recently. Look at the manpages of \"chmod\", \"chgrp\" and \"chown\" for details.
These are just the most basic things, the rest can be learned by exploration and experimentation if you have the time.
So that\'s it for starters, but there\'s so much more.
Personally, I use Debian (and OpenBSD for more security-critical things) (as if anyone actually cares what anyone else uses

). Oh yeah, and I have W98 for games.