Sorry I was a bit to brief:
I downloaded the site using htttack. Then I used calibre to read to index.html file. Afterwards I downloaded the index.html to the kindle. The result did not look nice and the kindle got somehow stuck when reading the generated book. I.e. it went back to the main menu. So something went wrong. However, I can't see in calibre where I have any control about the conversion.
In Mobipocket Creator I can add all html files by dragging them into the tool. I can set html tags for creating a table of contents and the conversion to prc format is pretty quick. The results looked much better than in calibre and did not crash.