This is a great question but very difficult to answer without specific information on the exact model of plasma you are looking at and also your current TV.
If you currently have a Sony or maybe a JVC, Toshiba or Panasonic then you probably have a very good picture now. That of course depends upon the specific programming and its broadcast quality and even the time of day.
Your new plasma will have to upconvert the incoming standard analog 480i cable signal to 720p or 1080i depending on the native resolution of your HDTV plasma. The higher quality plasmas such as Panasonic, Hitachi, JVC, Pioneer, NEC, Fujitsu, etc. (the traditional Japanese high quality brands) tend to have very good scaling circuitry which do a good job upconverting. Some of the cheaper brands (especially some of the Chinese, Taiwanese and Korean plasmas) might not do as good a job. LG and Samsung are at the top of this second list. Other brands many times are re-brands of these other units (if you can find out who actually makes them). Watch out: there is a lot of misinformation about who makes which off-brand plasmas and they change from year to year and also on the different sizes of plasmas.
I replaced two Sony 27'' conventional TV's with a 42'' EDTV JVC plasma and a 37'' EDTV Panasonic plasma which both have a 480p native resolution. The results are about identical in my case. Generally I would say the Sony's picture was in the good to very good range. The plasmas run from good to excellent. I prefer the picture from the plasmas. Even with a EDTV only plasma I sometimes get excellent pictures on programming that seems to be recorded with HDTV cameras and intended for HDTV broadcasts.
My overall comment is that I do have an mprovement in picture quality on my new plasmas over my old Sony's on the cable TV. I have only the standard non-HDTV signals from my cable company with no cable box. Also, you will have to strech the 4x3 aspect ratio picture of the standard programming to fit the 16x9 widescreen size of your plasma. Some brands do this much better than others by streching the ends the most and the center section of the picture the least. Again, some of the cheaper brands don't do such a good job here. Panasonic is reveiwed to maybe do the best with its ''just'' mode. I think my Panasonic is ever so slightly better than the JVC but they both are more that acceptable.
Hope this helps. Good Luck
I've been looking at several 42 inch plasma tv's and have three different answers to how plasma TV's will look with regular analog cable.
The TV's I'm looking at have built in HD as well as digital cable ready with cable card slot.
I understand that the picture quality will not be as good as the store model because I do not have HD yet. However, my question was "will the TV have the same picture quality as my current 32 inch TV when watching regular cable tv?"
Sears told me that it still has a good picture quality slightly below DVD quality.
Circuit City told me that without digital cable or satelite the picture would be very bad and I might not have picture at all. He said I might get just a blue screen. (not what I wanted to hear)
Bestbuy told me the picture quality wasn't nearly as good as the displays but shouldn't be anyworse then my current tv.
I was happy with the Sears and Bestbuy reply but I wanted the opinion of those that actually have a plasma tv. Please keep in mind I'm not comparing regular TV to digital or HD TV, but just want to know if the Plasma TV will produce atleast the quality I currently have with my standard TV. Thanks for reading all of this.
(Will most likely be getting Satelite but it might not be for a couple months.)