Well they are not always that old. I am writing this on an IBM that is running windows 98 and office 97. It has been given a new lease of life with a lovingly administered re-format and a bit of Irish luck that managed to defy the Internet modem and get it's self on line, with Broadband no less.
The reason I'm using this oldie is that the newer 2 1/2 year old computer has gone into hyper-drive and is blowing its AC adapter and running like an Ethiopian on a marathon the only trouble is it don't like it as much as the Ethiopian does. So at the moment it is in the sick bay and very soon it will be sent to a hospice for elderly computers and only let out again if it really makes an effort to run properly.
The main problem we are all facing with these machines that rule our lives is that they become slaves to the busy internet and whiz bang soft-ware that is cluttering up the works. No matter what you do they quickly take on a life of their own and then it is terminal before you can say gigabyte.