GIMP Gate

I'm just getting into making wallpapers for myself and also to give away. I know what resolution my laptop screen has and consequently what resolution to make a wallpaper for my own use. But how do you approach making various resolutions for others? Do you have to remake the wallpaper in different sizes? That seems like a huge pain. But if you don't, then how do you resize it without distorting it? What are the sizes that you make your wallpapers for general use?

Thanks in advance.