Ubuntu Desktop Edition allows users to perform common computing tasks like web browsing, email, document creation for free. It has a graphical installer that takes less than 25 minutes and provides security updates for 18 months on the desktop and 3 years for the long term support version. Over 30,000 software packages are available for free through the package manager and users can install additional software from third parties.
Points from: http://www.ubuntu.com/products/WhatIsUbuntu/desktopedition The bulk of business use for a computer is email, documents & spreadsheets. Some users need an image editor, CAD is even available in Linux.
Basically, Ubuntu will 'just work' for most uses on most hardware. Some of it may be more difficult to get set up, as you may need to find the right drivers and such. A search online will usually find you with a how-to that walks you through the processes.
The bug support and critical updates are where Linux really shines.
The package manager is very different then anything available to windows. It's like software update, but on steroids and with high-tech equipment to boot! There are over 30k packages 'built into' Ubuntu, that are simply a click away, with automatic dependency checking and update notifications.
What, REAL games? No way!
http://wubi-installer.org/
For the new Dell laptop, I tried to specify a latitude 6400 using both Linux and Windows Vista Pro. Dell's website is difficult to get 1 for 1 analysis between the two configurations. I could configure a laptop with Vista home for $34 more then the Linux laptop, and on a different configuration, I could upgrade Home to Pro for $58. Open Office is significantly similar to MS Office Pro to work as a replacement. Acrobat does have an open source equivalent at http://sourceforge.net/projects/pdfedit/ but I have never used it, so I don't know if you can get the same work done. Don't forget your annual anti-virus subscriptions. There are several studies available online such as http://www.cyber.com.au/about/linux_vs_windows_tco_comparison.pdf that demonstrate that Linux can be 19% to 36% cheaper to maintain for large systems.