If you want more of The Thornbirds then buy this DVD. It shows the years between the birth of Dane and when he is 10 years old - not featured in the original mini series.
Having not read the book, I'm not sure if this part is included, but it is enjoyable. It tells the story of Luke coming back to claim Dane as his son and a fierce court battle with Meggie for custody - no-one knows the true identity of Dane's father, except Meggie and her mother! There are more love scenes between Father Ralph and Meggie - wow, but somehow it's not quite the same! This is because most of the characters are different from the mini series. Only Richard Chamberlain remains and the chemistry with Amanda Donohoe, as Meggie, isn't as romantic as with Rachel Ward. What a pity the original actors couldn't have been employed again! Richard's obviously aged, 13 years after filming the first series, but he still looks good, considering!
If you're an avid Thornbirds fan, then it's worth a look at.