I'm trying to install some software. I believe that the easiest way to do this is to change the content of my sources.list file to include deb ftp://ftp.nerim.net/debian-marillat/ unstable main so that I can use apt-get to install software such as mplayer.
However, how do I do this since sources.list is a read-only file? (I know this is elementary, sorry)
Also, once I use apt-get update to update the list of packages, how will I know what the packages are called so that I can tell apt-get to install them for me?
Many thanks,
Ben

/etc/apt/sources.list is not read-only, it belongs to root so you have to be root to edit it. The same reason you need to be root for using apt-get. Once your root you can edit the file and add the line...

[code]
# MPlayer Repository
deb ftp://ftp.nerim.net/debian-marillat/ unstable main
[code]

Now are you running unstable ( sid ) or testing ( sarge ) or stable ( woody )? Since you'll need to change unstable to match whatever one you are using.

Then do apt-get update. Now to search what packages you want you can use apt-cache, try

apt-cache search mplayer

This will return amongst other things...

mplayer-386 - The Ultimate Movie Player For Linux
mplayer-586 - The Ultimate Movie Player For Linux
mplayer-686 - transitional dummy package which can be safely removed
mplayer-fonts - Fonts for mplayer
mplayer-k6 - The Ultimate Movie Player For Linux
mplayer-k7 - transitional dummy package which can be safely removed
mplayer-nogui - The Ultimate Movie Player For Linux

You can use which ever of the above is best for you. When you do install mplayer it will also give you a list of suggested packages

w32codecs, libdvdcss, mplayer-doc

I'd install them as well.

Can't you just aptitude install unstable....I'm new to apt also.

I don't think you can do a dist-upgrade, and/or source changes with aptitude.

If you are confused about the sources.list. Go into the directory "/etc/apt". In there will be a file named "sources.list". Edit it using VI or Nano or Emacs or whatever your favourite text editor is. You will open up this file and a small list of URL's will be displayed. Add in:
Overwrite the existing configuration and go back to your prompt.

Type in:
This will update all the package libs that will be available to you.