It depends on the DVD player and what quality the upconverter is. CDCi by Faroujda is a fairly good one or the HQV Reon is one of the best but you will pay more for the players with it.
If the Player has upconversion it most defiantly is progressive as all of them will at least do 720p or 1080i all the newest ones of good quality also now do 1080p does your display support 1080p?
I guess I should explain what the difference is between progressive and interlaced video.
Think of your display as a divice with lines from the top of the screen to the bottom, Interlaced shows half of an image (on the odd lines of pixels) every sixtieth of a second, and then it shows the other half (on the even lines) the next sixtieth. Therefore, it takes one thirtieth of a second to show a complete frame, giving a framerate of 30 frames per second.
Progressive scanning shows the entire image every sixtieth of a second, so the framerate is twice as high - 60 frames per second.
So progressive scanning creates a smoother image, and is preferable if you have a choice particularly for fast moving images like action or sports with alot of camera pans.
But this fully depends on the processor doing the conversion in the DVD player if its cheap then you may be better off not using it at all.
.
