ID can only Place jpegs, not open them.
That's strange, when I was working with the trial it was actually possible to open the jpeg files. Should I convert them? Or will the quality of the photo's be the same when I place them in a blanco file?
You are mistaken. InDesign has never been able to open any type of image file directly. Prhaps you had the trial for Photoshop or Illustrator, both of which can open jpeg.