Is there any difference in picture quality if you use a sd-stb or a hd-stb on a sd plasma hooking up to the exactly same input (eg. component, dvi)?

Yes there is. The HD box looks better (if the source is HD).

Some reasons for this are:
1. The HD box puts out a higher quality signal, and often has superior processing on SD compared to the cheaper plamas.

2. SD displays are 853 pixels wide and SD transmissions are only 720 (or less). So if you have a 1440 HD source and scale it down to 854 this will be better than scaling 720 up. Also, 1080i has 520 lines per field whereas SD has only 288. Given that SD plasmas (to the best of my knowledge) scale each HD field to 480 and display progressively that's quite a lot more information that's displayed. Compression also comes into this, as SD is more compressed than the same signal up converted to HD (except on the ABC, SBS and Seven!)

3. HD boxes have better connection options, like DVI or VGA. With SD it's either Scart or component.

[quote=ChrisM,Mar 17 2005, 07:40 PM]
I can vouch for everything said by Chris. I briefly had a HD stb to a SD plasma and it was much better than my current SD picture. (Swapped it as I wanted a PVR and the HD versions are only just coming out now and are very expensive).

Best bit about HD stb was DVI connection.....much better than component, which I'm running now.....