The recent article: "Built-in Obsolescence, by Margaret G." prompted me to comment on personal computers. I am a die-hard anti-Windows guy. The troubles caused by the easy subversion of your own computer by bad people combined with terrible permissions allowing user space programs to affect and jump to your whole network makes it a no-go operating system for people wanting reasonable network security unless you are a computer scientist working for the NSA or other governmental agency with a contract which allows you to review and customize the actual source code. While most windows boxes die a slow slide to uselessness caused by inadvertently or surreptitiously installed spyware, malware, and junkware running in the background you you can often revive it by wiping the hard disk and reinstalling windows if your manufacturer is one of the few that gives an install disc or avoid the entire problem by never allowing MS Windows computers to connect to the Internet or allow any outside disks to be inserted or connected for any reason.
Breaking through the new OS Unix/Linux learning curve no matter how shallow is an investment in time, install on at least one computer so you can get familiar with it while you have access to Internet help forums. Just so you know I have my best responses from people who are power Unix users and from people who only know how to surf the web and I install Ubuntu so they can use a morally clean install disk.
For most people I suggest Ubuntu Linux because most functions work automagically such as Wi-fi, 3G phone modems, and many advanced video cards. Not everything works perfectly with all hardware since the manufacturers worry most about the large MS Windows market, but the beauty is you can order or burn a free Ubuntu Linux CD and test it out without even doing an install. If you need MS Windows for special software there is an option during install to dual boot at startup into Linux or an existing Windows partition. The good news is almost all Linux software is free and there is no moral or ethical questions in borrowing or burning the install disk since the writers are bound by contract law to release all distributed updates to GPL software for free. If the computer runs too slow you can always use IceWM window manager and lightweight apps such as AbiWord as opposed to richer ones such as OpenOffice.org office suite.
For really old hardware DSL Linux is a good choice. Although you need some more command line Linux knowledge to run DSL on some computers it includes drivers for older hardware and uses a simpler interface suited to slower machines all the way down to 20 year old hardware in the 486 class.
The main concern is hardware failure in computer moving parts and in the power supply. Having spares for hard disks, optical drives, and cooling fans are top priority as are protecting the screen hinge joints and hinge connection cables on laptops. Knowing how to improvise and repair a DC power supply and connector jack or better yet having one on hand will make the eventual connector failure not such a big deal. High voltage systems like the cold cathode fluorescent tube inside a laptop are occasional failure points although you can improvise with a few white LEDs in a pinch; even worse is the fragile power hog vacuum display tube in non-flat screen monitors.
If all else fails having an Live CD type install CD or USB drive means you can still boot and use your computer as a Linux machine even if the hard disk is destroyed.
My best luck has been with used business grade computers. Business grade mostly computers have better components since they don't want to send out a same day service tech that often, they also tend to have well supported hardware when using Linux.
As an aside I find Wikipedia is a very useful basic reference, I keep an offline copy of a recent snapshot of Wikipedia on most of my machines. MS Windows users can grab a local copy using WikiTaxi. Most Linux users can install Wikipedia Dump Reader from KDE.
I have the KDE Wikipedia reader installed on my Eee-901 and it takes up about 6GB of flash disk space, this combined with a 25w solar panel, DC charge controller cable, an external disk drive, a radio terminal node controller, and a 3g modem and I can be truly wireless. Shalom, - David in Israel