I have a friend who's got one of those DVD players. The output looks pretty much the same on a PC CRT regardless the video is played by the DVD player or PC DVD drive.
I read somewhere that progressive scan is supposed to give you better picture quality coz it eliminates the picture interlace problem. Of course your TV set must support progressive scan in order to enjoy this benefit. As for progressive scan on PC CRT, I think it should enhance the picture quality as well. But unfortunately I can't verify this, as my friend's machine is a non-progressive scan version.
Don't know of any DVD players but I use Viewsonic's <A HREF="http://www.viewsonic.com/products/video_box_vb50hrtv.ht..." target="_new">VB50HRTV Tuner Module</A> to watch DVDs on my computer monitor and as the name implies I also use it to watch TV. The computer does not have to be turned on. The VB50HRTV has one RF input, one RCA video input, one S-Video input, and one pair RCA stereo audio inputs. Outputs video to your monitor and sound to your PC speakers. It costs about $100 USD.
DVD viewing is good, better than an average TV. It's not as good as DVDROM playback on the same monitor. TV viewing is very sharp with good color. Because the picture adjustments on the VB50HRTV are very course I found I had to do a lot of fussing using the monitor's controls to fine tune brightness and contrast. Contrast ended up being a little higher than I would like it for computing. Unfortunately, my monitor doesn't have multiple profiles.