Looking at the manual (pg 102 for the HDC-DX1P/PC) you can only transfer still images from the memory card to the computer via USB.
With a mini DVD disc camera you should be able to get the video off the disc by putting the dsc into your DVD drive and use Windows Explorer to transfer the video files to the computer.
The other option is to use the cameras playback of the disc and capture via a USB video capture device however this is not as good as copying the files direct from the DVD.