As I promised, here are step by step the actions that I carried out once I installed KDE 4.6 in my dear Debian Testing. I've been a bit busy today, so excuse me if it's not as detailed as you'd like.
Today morning I did a clean install (from scratch) of Debian, to better document the packages I need to install and so on, so if you follow this article step by step, you will have no reason to have any problems.
Debian installation.
With regard to the installation there is a peculiarity. I normally use Debian Testing and the most logical thing is that I have downloaded an iso of this link and with that you have completed the installation. The problem is that since my bandwidth doesn't allow it, I had to use an iso of debian-squeeze.
Recommendation # 1: It tries to install with the Debian Testing iso for two reasons:
- There will be fewer packages to update.
- You run less risk of encountering dependency errors or things like that.
Installation, either with iso de Squeeze o Wheezy, it is exactly the same as how I explain it in this pdf, except I don't install Graphic Environment, but only the Standard system utilities. For this guide I am going to assume that the installation was done from the iso of Testing.
Update
Once we finish installing without a graphical environment, we log in as root and configure the repositories:
# nano /etc/apt/sources.list
in the sources file we put:
deb http://ftp.debian.org/debian testing main contrib non-free
and update:
# aptitude update
When finished, we update the packages already installed:
# aptitude safe-upgrade
Once this process is finished, if everything has gone well, we restart the PC and we went on to install KDE.
KDE installation
In this guide we are only going to install the necessary packages so that KDE is displayed correctly and be able to use it. We will also install some necessary packages that are not included by default. Once we log in as root, we will have a fully functional environment by installing the following packages:
# aptitude install kde-plasma-desktop kde-l10n-es kde-i18n-es kwalletmanager lightdm
With this is enough so that once it finishes and we restart, we can enter our brand new desktop. If you look at the end I added LightDM and I explain why. When we install the package kde-plasma-desktop, this installs us KDM which for me is very heavy, so I replace it with LightDM. Once we give Enter, the wizard will ask us which one we want to use, you choose the one you want.
LightDM it will also install the packages for the graphical server. Since I use intel, I just add: xserver-xorg-video-intel, being this way:
# aptitude install kde-plasma-desktop kde-l10n-es kde-i18n-es kwalletmanager lightdm xserver-xorg-video-intel
This is enough, but if we want we can install once it finishes, or together with these, the following packages:
# aptitude install kde-icons-oxygen kde-config-gtk-style kde-style-qtcurve kwalletmanager kde-icons-mono system-config-gtk-kde gtk2-engines-oxygen gtk-qt-engine
They are packages with which we will improve the applications gtk that we use and some icons that we add. If you don't use the wallet KDE to manage passwords, you can remove kwalletmanager.
Additional packages.
Before restarting, it would be good to install other packages that we may need, for example:
Audio / Video Related Packages
# aptitude install clementine kmplayer vlc (instalado por defecto) gstreamer0.10-esd gstreamer0.10-ffmpeg gstreamer0.10-fluendo-mp3 gstreamer0.10-plugins-bad lame pulseaudio -y
System utility related packages:
# aptitude install ark rar unrar htop mc wicd wicd-kde dbus gdebi-kde rcconf ksnapshot -y
NO / KDE applications I use:
# aptitude install iceweasel icedove libreoffice-writer libreoffice-l10n-es libreoffice-kde libreoffice-impress libreoffice-calc gimp inkscape diffuse -y
Things I remove:
# aptitude purge exim4 exim4-base exim4-config exim4-daemon-light -y
Obviously you should add or remove what you need 
Customizing KDE
If we pass the previous steps without problems, we come to the most interesting part of this whole thing: customizing KDE to save us a few Mb of consumption. First we will do it manually (by console) to later move on to the graphical aspects.
Deactivating Akonadi + Nepomuk:
I will not go into details about what it is Akonadi o Nepomuk, especially because there is an excellent article that describes very well what the function of each of them is. You can read it here. To deactivate Akonadi completely, we do the following:
$ nano ~/.config/akonadi/akonadiserverrc
We look for the line that says:
StartServer=true
and we set it to true:
StartServer=false
Keep in mind that applications such as kmail they use Akonadi, so we may not be able to use them. To deactivate Nepomuk edit the file:
$ nano ~/.kde/share/config/nepomukserverrc
and that:
[Basic Settings]
Start Nepomuk=true
[Service-nepomukstrigiservice]
autostart = true
We leave it like this:
[Basic Settings]
Start Nepomuk=false
[Service-nepomukstrigiservice]
autostart = false
In theory all this can be done by The Preferences of the System, but nothing, it's faster here 
Eliminating effects.
We can save a bit of resources by eliminating the effects (transparencies, transitions) that comes in KDE by default. For this we open the System Preferences Manager » Appearance and behavior of the workspace »Desktop Effects and uncheck » Enable desktop effects.
We can also remove other effects by configuring oxygen-settings. For this we press Alt + F2 and we write oxygen-settings. We should get something like this:
There we can entertain ourselves removing effects of various types. I simply uncheck: Activate animations.
Properly displaying Gtk applications
The first thing we do is install the motors gtk necessary:
$ sudo aptitude install gtk2-engines-oxygen gtk2-engines-qtcurve
Later we open a terminal and put:
$ echo 'include "/usr/share/themes/QtCurve/gtk-2.0/gtkrc"' >> $HOME/.gtkrc-2.0
$ echo 'include "/usr/share/themes/QtCurve/gtk-2.0/gtkrc"' >> $HOME/.gtkrc.mine
Now we only have to select in the KDE preferences than for applications gtk use QtCurve. The result can be seen in me Firefox:
Eliminating processes at the beginning.
We open the System Preferences Manager »System Administration» Startup and Shutdown »Service Manager and uncheck the ones we don't want to start. Example of one that I always disable: Nepomuk search modules.
Eliminating elastic cursor.
Although it may not seem like it, the little jump of the icon that appears on the cursor when we open an application consumes resources. To eliminate it we open the System Preferences Manager »Common appearances and behaviors» System and app notifications »Launch notification and where does it say Elastic cursor we put: No busy cursor.
Classic desk.
I have always liked having the traditional desk, as in Gnome o KDE 3. For this we go to the desktop and click on the icon in the upper right part and select Folder view preference:
And in the window that comes out we change the disposition to Folder view.
RCConf
We installed rcconf to disable as usual some daemons that start when the system boots. In my case one of the ones I delete is KDM since I use LightDM. You have to be especially careful with this, and never delete dbus.
And so far this guide. I hope I can add more things as time goes by.