PC without Windows or Microsoft! Like this:

Debian comes on a set of installation CDs - free downloadable or to order by mail. The basic system requires only the first CD. Further software (e.g. word processor, spread sheet etc. just like MS Office) is scattered across the other CDs (e.g. for the equivalent of MS Word search for "openoffice.org-writer" at http://www.debian.org/CD/jigdo-cd/#search). Although with some expertise you can in principle install any Linux software, it is highly recommended to only use the software "packages" specially vetted by Debian. The following instructions refer to the old stable release of debian called "Etch" (2008).

My own experience:
 
1) Installation: the PC (mine was a Dell desktop, made in 2002) is booted from CD 1; installation process asks for some basic settings (keyboard layout etc), but don't set up a network connection yet. Two user accounts with passwords are set up, one for the average user and one for the administrator to install further software and change important settings.

2) Getting used to the new user interface: look around in menus, change appearance of desktop ("themes"). Basic stuff: Desktop->Preferences->Theme; Desktop->Administration->Synaptic Package Manager; things like CD burner, USB and sound work straight away after installation from CD 1.

Synaptic Package Manager: shows a list of available software, to which you add CDs from the set (Settings->Repositories->Installation Media->Add Cdrom, then Reload). Choose from list, mark desired programs for installation, then press "Apply". You can also specify an official Debian download site as source of software, which may be more convenient than having your own copies on CDs, but see 3) for added safety.

3) Before connecting the network/internet: install firewall software "bastille" and required Perl-Software for it; then  Applications->Debian->Apps->System->X-Terminal as root. Enter bastille -c in the terminal. Answer all questions (defaults are ok...), finally answer 'Yes' to save settings and boot with them every time.

4) Connect the internet (Ethernet cable from modem in my case), network connection sets itself up. Now the built-in browser ("epiphany") and Email/News ("icedove" = Debian-Thunderbird) will work as well. Note that everything also works (with less security) without step 3).

5) Linux shell: this is technical stuff under the bonnet... all the technical details in Debian are controlled via command lines in the shell or terminal (similar to the old DOS prompt). Always read help text for commands first, e.g. by typing "man bastille" for bastille. In case of a massive problem/mistake, simply reinstall Debian from CD 1 (no big deal). This happened to me when I tried to install "hotplugs", which was already installed (kernel messed up afterwards...)

6) More technical info e.g. from http://loll.sourceforge.net/linux/links/index.html.

Notes added in 2009:

7) Tried the latest version of debian: "Lenny". This version also contains an swf player (swfdec) for the web browser, so that embedded Flash movies can be played without using the commercial player.

8) WLAN with USB-Stick: The Debian PC now also works without ethernet cable using a wireless USB stick. There are USB devices which don't require commercial drivers, but mine was a cheap one using the RT2501 chip (Ralink). There are "non-free" drivers to download in Debian at no cost. See wiki.debian.org/WiFi. Once the connection is established, go into bastille and define the wlan interface and allow IP address spoofing. 
WLAN security: activate encryption with WPA (WEP is too weak). Sample configuration file: /etc/network/interfaces  
See documentation under /usr/share/doc/wpasupplicant (part of local file system).