> I'm very new to Linux. I have Red Hat 7.3 installed (with Gnome and KDE). 
> 
> I've noticed that across SOME applications, copy and paste works, and 
> across others, it doesn't. Is there any rule that applies, and is there 
> anything like the Windows "clipboard" or the equivalent (if I knew what I 
> was doing).

    It would help if you could mention which programs do not work. Many of the
older programs have this problem, and the 2.0-2.2 versions of KDE had trouble
correctly pasting to GNOME programs. However, as of KDE3, this has all gone
away. (I don't know what version of KDE RH 7.3 uses.)
    In the meantime, there is a universal copy-paste method that, in the long
run, you will use just about all the time because it is so much quicker and
easier. Highlight the text you want to copy, move to the window that you want to
paste the text in, and press the middle mouse button. (If you only have a
two-button mouse, you can emulate a third button by pressing both the right and
left buttons at the same time.) Voilá!
    Technically, X has two "clipboards." One is for the ctrl-c, ctrl-p variety,
the other for the highlight-and-middle-mouse-button variety. That way, you can
have two different texts stored, which can definitely come in handy at times.
    I should also note that if you are using KDE2, a "klipper" utility is
started in the system tray that was intended to overcome the problem of pasting
to GNOME programs. If you are using KDE2, try clicking on it to find out more.
    :Peter