TOPIC:

I made a new installation of Xerte on an new laptop. Somewhere else I have a folder with old userfiles I want to see again. Is there a way to import that files again in my new installation?

If your old install is working, just export and import the zip.

If not, for each project you want to import, create a new project in the new installation and then copy the data.xml, preview.xml and the contents of the media folder over the just newly created project.