Well, DVD is a far cry from HDTV. It is actually standard definition televsion and while progressive scan may help some, you will never achieve anything approaching the quality of actual HD material.
You may want to set the DVD player to progressive scan (which you may have already done) and see how that looks. In the end, the DVD player may just not be of high enough quality to give you the best image.
You may also want to try different discs and use a calibration disc like Avia or Digital Video Essentials to optomize your DVD player and television.
Finally, if your TV is a HD model with DVI or HDMI inputs, you may want to look into getting a decent upconverting DVD player that converts DVD material to a higher resolution output. It can never actually make the video HD, but it can look great. I am unsure which brands to look into, but there will be lots of advice on that.
Please respond with your exact brand of DVD player and television (not just the manufacturer) and you may get some feedback on potential issues with the actual equipment you own that may help you out.