Several million Pentium PCs currently end up in UK landfill sites each year. At the same time the minimum hardware requirements for much Open Source Software continues to increase. For example in 2002 there were then several current packaged releases of Linux that had no difficulty running on a Pentium II PC or equivalent. Today in 2005 it might be possible to install some of the current releases on such a machine, but only someone who has an interest in slow-motion would appreciate the end result at run-time. Also unlike an older car or computer monitor an older PC generally uses less not more power than a newer one.
Although an older version of Linux is still fairly secure compared to some other operating systems it is not likely to have the level of support enjoyed by more recent versions. It can for example become an extremely time consuming business to get drivers for some hardware using older releases and dependency problems between releases are common. On the plus side it could be argued that because the code is open a user has in theory a chance to overcome such problems. However that kind of user will almost certainly need above average technical skills to do this, which means that most users will go for the easiest option of upgrading the hardware to match or exceed the minimum requirements of the latest software.
In some cases it maybe possible to get a reasonable run-time result using the latest Open Source Software on older hardware by adding more memory. Other upgrades such as adding a more powerful processor to an older board can only be taken so far, but in any event this leaves the environmental problem of what to do with the replaced component.
I might suggest that there is money to be made from a potential market need to develop Open Source Software that successfully tackles minimum hardware requirements in the most environmentally friendly way. There are many who claim that the use of Open Source Software is already extending the life of computer hardware, but in my view there is considerable potential to do more.