FWIW, I'm probably going to get shot for saying this, but in my mind there should be no perceivable difference in quality between an "i" signal and a "p" signal of the same resolution. In other words, turning off progressive scan on your DVD player will cause a 480i signal to be sent to the TV (which it accepts). Turning ON progressive scan on the DVD player will cause the signal to be output as "480p".
My wee brain tells me the ONLY difference between the two has to do with "flicker" and doesn't actually impact picture quality otherwise. If you have ever had a DVD movie sitting on the static intro screen on the normal TV, you probably noticed some flicker to it (not everyone will see it). the "p" eliminates this flicker, but it has never been a problem for me when watching an actual movie (not static image).
So I say keep your component cables (as its a better connection that composite or S video), throw your DVD in interlaced mode, and enjoy the movies. And if your really insistant on getting that "p" mode to work, better start shopping for a new HD TV!
-Alan
