In a few days time, we are upgrading computers and we will probably be looking for bigger, faster and better computers. As it is the case for hundreds of other companies in the country, the machines will have their contents wiped and this includes the operating system, whose license is not transferable.
Linux.com has an interesting article on how to run Linux on older hardware. The bottom line is that you can run Linux on almost any kind of platform, even those twenty years old although you will have to make compromises in those cases. It is a noteworthy trend in that Linux does provide with a fallback solution whereby you can always switch to a less demanding Linux distribution if your computer is less powerful.
That is in stark contrast with what Microsoft Vista, for example, will deliver. You will need a faster, more powerful, more expensive machine to run it. Granted it will have a refined user interface and more security options but you will basically do the same things you were doing since Windows NT4, that's more than a decade ago.
If your needs are not particularly demanding or specialised, Linux might be the kind of "upgrade" your computer will need if your budget does not allow for expensive replacements.
Another beautiful thing with Linux and older hardware is that you can recycle and reuse obsolete computers that would otherwise be discarded or dumped. With relatively little knowledge, you can convert that old Pentium II of yours into (a) a Media Centre à la Microsoft Media Centre Edition (b) a hardware firewall (c) a standalone wireless file server or (d) a Linux Terminal.
More importantly, even if you do not have that old computer, you can always buy one for cheap and try to play with it. I've recently purchased a second hand Apple Mac G3 computer and I'm looking forward to install Yellow Dog Linux on it.