I got 3 of the albums from amazon.com, and the 4th one I got when I saw them here in Chicago.
Which track do you have? 3 of their albums are folk-based. The other, "Hildegard von Bingen" is based on the writings of Hildegard and is quite different (but still good).
My favorite album is Vengeance (I forget the name in Swedish), closely followed by Guds Speleman. I've only listened to Vittrad twice, so I can't give much of an opinion on that, but I don't like it as much. And Hildegard is good, but completely different.