XP/SP3 is a good OS - no doubt about it, as witness the hundreds of thousands of people who are still running it and their businesses successfully.
The key to XP/SP3 stability is stripping it down, only installing the apps you really use and avoiding peripherals with unstable device drivers.
Charles Sparks (aka Blackviper) has an excellent website -
Black Viper’s Windows XP x86 (32-bit) Service Pack 3 Service Configurations | Black Viper | www.blackviper.com - which details services that can be which can be disabled or started manually and offers different configurations. It is amazing how much you don't need or whose startup can safely be delayed.
Soluto -
https://www.soluto.com/home - is useful, just disable it when you have done your optimisations.
There are almost certainly Windows components that you don't need/use - examine Add/Remove Windows Components and prune.
Reverting to the Windows Classic Theme in XP saves a lot of cycles
"Use the Windows Classic Theme in Windows XP
If you want the Windows Classic desktop feel and functionality, you can change the desktop theme to the Windows Classic theme:
Right-click an empty space on the desktop, and then click Properties.
On the Themes tab, click Windows Classic in the Theme box.
Click OK.
Change the Windows XP Start Menu to the Classic Windows Theme
To change the Start menu to the classic Start menu:
In Control Panel, double-click Appearance and Themes.
Click Taskbar and Start Menu.
On the Start Menu tab, click Classic Start menu, and then click OK."
Also disable most of the eye-candy (Adjust for Best Performance) in System/Performance.
You can probably junk a lot of fonts (leave the System ones!).
Avoid later versions of MS-Office (I still use 2003 - though really just for Powerpoint)
Libre/OpenOffice are memory hogs on older PCs/XP - consider using a simpler and faster WP like AbiWord (and see -
Best Free Word Processor). You should also try using IBM's Lotus Symphony which is free, fast, modern and surprisingly resource light (and, amazingly, renders Powerpoint accurately).
As a browser, Chrome is excellent, though I have a weak spot for Opera, with its built in brilliant email client.
For anti-virus, the lightest footprint and most stable is undoubtedly Microsoft Security Essentials - it isn't perfect but plenty good enough. Schedule a weekly scan with Malwarebytes Anti-Malware and you're good to go.
CCleaner will decrapify the system and tidy up the Registry - makes a big difference.
Finally, the XP Firewall is fine, but usually misconfigured - see
How to configure the Windows Firewall feature in Windows XP Service Pack 2 and get it right.
Mac
Edited to add:
I'm not suggesting people
should stick with XP, just trying to help if for some reason they can't.
XP was good in it's day, streets ahead of 98SE but it is now showing it's age; creaky, less stable than Win7, less secure, and support by MS and hardware vendors is waning.
If you
must have it, then it's best run in a VM like Windows Virtual PC or VirtualBox.
