If anyone feels they *must* run an end-of-life operating system, they should understand there are some serious security risks, and take precautions. Even if the OS works stable for you and performs decent, they are filled with unresolved security exploits. Even the design of Windows XP SP3 is fairly easy to exploit these days. Windows 7 and 8 have had a lot of changes and security additions made to make them much better than the older Windows. They aren't perfect, but no OS is.
I agree with some about using a Linux distro, such as Ubuntu, Debian, CentOS, RedHat, etc. if you have no specific need for Windows applications. You will have a more secure and current operating system that will likely perform better on old hardware. I only recommend this to novice computer users if they primarily use their computers for web surfing, email and other basic functions. If you need Windows applications to do what you do, then you need to make sure there are Linux equivalents, or just stick with Windows.
Ubuntu is my favorite Linux desktop OS, and I use Ubuntu and CentOS servers daily in my work.
I'm finally getting the last of my foot-dragging clients to move from Windows XP after all these years. It was a great OS, one of Microsoft's best, but that's just not the case anymore. Under no circumstances would I run anything from the Windows 98/ME era today.