Boys and girls, I do know how to make windows open certain files with paint.net.
I did it by hand, because it wasn't done automaticly during installation. That's why I thought there was something wrong with my installation.
On the other hand you have something in Vista which is called in dutch (my language) "standaardprogramma's", in english Default Applications. With one mouseclick you can for instance make that your default application is the one that opens all filetypes it can handle (so not by doing it by hand for every file type in the options folder as explained Hitman-X).
But in the screen of the default applications there is no option for paint.net as an image-editor. I read on The Net that only programs which register themselves in certain ways according what Microsoft wants with the right kind of API's are listed as possible default applications. And as there are only very little programs shown as options in the default appliations window, I think paint.net and a zillion other programs are just not (yet?) capable of registering itself as a default application.
By the way: Firefox nowadays does. :wink: