Thank you, all. :)
I have tried several things before posting here, including checking various forums. However, for people having Windows XP, all I have ever found out was I'd have to reinstall the system.
All suggestions involving a download of any software requiring the Windows Installer to install will not work. Unfortunately, most publish their software to install using the Windows Installer, so that will never work.
I am going to check the forum links above (German) now and will see.
My real problem is: What do I do with the software (e.g. PDF Editor) that I bought online, downloaded and installed years ago, when I need to reinstall Windows XP? All those softwares will get lost -- "of course" I never made any recovery discs, plus, I have not saved the activation codes as some of those softwares are like ten years old. When I reinstall Windows XP, I will not be able to reinstall those softwares. :(