The OS is still the same, so the method of installation is still the same as it was in 2002: login as administrator and run the installer program (usually an .exe or a .msi).

Some current installers might say they aren't compatible with Windows XP. Then you install an older version or a comparable program that is compatible.

It might be time to consider a move to Linux, Windows 10 or MacOS on your new systems. But as long as you're happy with what you have and it all works, there is no real need. But be sure to have a good backup of your office data.