The problem is that you're mixing video formats, and you may not have your project set up ideally for any one format.
If you're planning to output a DVD, which is standard def DV, you might as well work in DV.
Your HDV (tape-based) camcorder should have the option to output your HDV footage is standard DV.
Make sure your Premiere Elements project is set up for standard DV and add both your HDV's standard DV footage and the DV (from a miniDV tape-based camcorder) to it.
If you're not mixing video formats and have your project set up for your video format, your DVD should produce excellent results.
Thanks for your advice. In the future I will use one format in one project. But my question is how can I change the settings of my existing project? Or, if this is not possible: can I copy-paste my current project to a new project with different settings?
For the most part, you can't change your project settings mid-project. (Some people have "hacked" the .prel file in Text Editor, but I'm not sure of the specific steps.)
Others have used a program called ClipMate to cut a the video from one project and paste it into another. Once again, I've no personal experience doing this, but many people have reported success.
There are folks on the Community Forum at http://Muvipix.com who can offer more specific advice.