Sure thing.
Basically, you have two main options to install software in Crunchbang. Mainly, you will be using a an application called Synaptic. This is a graphical installation environment that is pretty self explanitory. For now, though, we'll be opening up a command prompt and installing a few essential packages.
Start by right clicking the desktop. A menu will appear. Go down to "Terminal" and click the left mouse button. This will open up a prompt for you.
From here, you will have access to a set of scripts known as APT. (Debian Advanced Packaging Tool.) To install any software in a GNU/Linux operating system requires superuser (otherwise known as root) privileges. As we will be installing a few packages, start off by typing:
This will change our "user" prompt flag from $ to # (The # signifies that we hold superuser privileges.)
Now, to use APT.
First off, check out these pages:
APT Tutorial and
APT cheat sheet.
Right, let's install a package. We'll start off by pulling in a sane web browser. (I am unsure how much RAM this computer has. Both Firefox and Chrome are pretty memory intensive. As a result, I generally opt for a much more lightweight browser.)
At the command prompt, type:
Once this finishes, the package will be available. You can start it by holding down alt and pressing F2. This will bring up a run dialog. In here, simply type midori. Our new, fast browser will now load.
You can easily search for packages with APT in the following fashion:
Now, as for Mudlet. You have two options here. You can either use the pre-compiled Linux binary (Although at this stage, only version 1.1.1 is available.) You can get this
here.
Save that to /home/<username>/downloads.
To install this package is a little different than with using APT. Because it is a binary package (Not a Debian package) we need to install in the following fashion:
Type the following:
This will drop superuser privs. We don't want this right now.
This will change our current directory.
This will change the file permissions for the Mudlet download. Right now, the permissions do not allow the file to be executed. (Only read.) - Read
this page for more information of file permissions.
This will execute our file and run the installer.
Should you require a more up to date Mudlet, this will require a lot more work. (Installing multiple packages and compiling some source code.)
As for your brightness issue. I am unsure as to what is causing this. Is the problem persistent when you load an application? The default desktop background in #! is pretty dark. You can change this by right clicking the desktop and selecting Settings -> Openbox -> GUI Config Tool.
Hopefully you have enough information there to get you started. If you have any problems, don't hesitate to poke me and I'll see what can be done.
Good luck.