It is possible you have field dominance settings wrong in making the DVD. In PAL everything in upper field dominance except DV codec.
Unless we have some basic info about how you are making your DVD, we can only guess at this stage. Check your work flow from the sequence settings through to the DVD burn process. The field switch will be in there somewhere.
Deinterlacing seems to be the mantra to fixing this common issue but it is throwing away resolution and potentially creating motion artefacts on movement. Creating a progressive look is another issue but must be thought about before shooting, not after.