DVD's are far inferior of HDTV/Blu-Ray in my opinion. DVD's are 720x576 resolution MPEG-2 video while HDTV is 1920x1080 (or 1440x1080) resolution MPEG-4 video and Blu-Ray even has a much much higher bitrate than HDTV.
If your DVD player claims to output HD, then it must do what is called...