I'm looking for recommendations for distro & DE for a new small business office

Problem is most of the people here are in their 50s & used to Microsoft's "point & click/double click/ right click" GUI, hence it may be almost impossible for them to familiarize with commandline even if you try to teach them all day

The Desktops we use are

HP Compaq 6200 Pro
-i3-2120 3.30GHz
-2GB DDR3 SDRAM
-250 GB 7200RPM Serial ATA/300 Hard Drive, 3 MB cache
-Intel HD Graphics 2000

So which distro/DE is the most user-friendly & out-of-the-box for such?

Kubuntu -12.04
or Ubuntu-12.04

Decide on packages before hand and do a kick-start install if there are too many machines

Ubuntu for the office? No. You want something stable and reliable. CentOS is a free version of Red Hat, which the large US companies buy. Get the DVD version, not the CD. Install it with the Gnome desktop on one computer and the KDE desktop on another, and ask people which they prefer (that gets them interested and makes them feel valued). Then standardise on one.

As for the command line, only the person who looks after the computers need ever use it. Launching programs and opening files is point and click in Linux too. And don't worry too much about the office staff. Someone of 55 would have been 28 when the first version of Windows came out, so they've seen quite a bit of change. Setting keyboard shortcuts is a good idea. My keyboard has the usual email and www buttons, and I use the "favourites" one to launch the office suite. You can also use the Super keys (aka Windows keys) to speed things up: e.g. I have Super+a for accounts, Super+f for the file manager, etc. You can even set a shortcut to open a specific file in the program being launched.

CentOS will be relevant if there is a need to run servers. Otherwise if it is all about desktops + LAN, then the desktop editions of *buntu or any other non-bleeding edge distro should be fine. Ubunutu-12.04 LTS will have 5 years of support.

I don't think that Ubuntu can be considered an enterprise distro. It's true that the software is seldom actually broken, but it's too changeable. And is Unity really suitable for office use?

For a free, reliable distro it's going to be CentOS, Debian Stable, or Slackware/Salix and CentOS is the easiest of the three to manage.

Welcome to the forums!

My recommendation is Windows (unless you have a specific reason for wanting Linux?)

M$windows is evil in a billion ways, and GNU/Linux is better... but, yes it is better if you know some of the reasons beforehand.