It looks like this game doesn't work on SD TVs 576i specificaly, don't know about 420p.
Definetely something I want support for. Ultimately we should keep the internal rendering to 720p, and scale it down/up from there. That way nothing changes in the game play.
This is how I would solve this, from the top of my head. I would update PARAM.SFO to support more SD resolution, but keep > 720p unsupported, since I think all HD screens support 720p. (likely another dumb assumption though ;). The problem with rendering at 1080 is the debug font which doesn't scale, and becomes microscopic in size. Then I would update the score rendering with a few switch/case statements for the different resolutions.
The problem isn't with the resolution, but there are TV screens that do overscan, so simple fix like changing paddle position fixes the job. Same is with the scores, it overscans to both side, width and height adding aditional button to change paddle/score postion would fix all the problems, to be honest that's what I did, in a harsh way, changed position for it to work on my screen.