I am not familiar with the details of the DVX100A, but if the camera has a way to feed the DVD footage from a DVD player (RCA cables to camera, RCA cables to AV plug, etc) and the camera can be used as an analog to digital convertor, then you can play the DVD into the camera and then back out over firewire to the computer and capture as an AVI file. I have done this many times using other camcorders. Be aware that you are still taking a compressed format from the DVD, so the quality of the AVI file will not be the same as the original footage.
You could also try copying the VOB file directly from the DVD and renaming the extension from .VOB to .MPEG and try bringing that directly into Premiere. I don’t remember how PPro 1.5 handles this. I have had mixed results trying this method.