Whats the difference between HD and non-HD resolutions?

[cannibalica]

I see everywhere that HD resolutions are 720p or 1080i, but the manual of my non-HD Tv-set Panasonic 42PA50E says that it is capable of showing those resolutions... So far I haven't been able to produce anything better than TV-out from Geforce 6800, because tv has no DVI or VGA inputs, so I didn't seen the quality difference myself. So, what's the difference?

[Baldrick]

It is capable of showing most resolutions but it will be downsized to the TVs max resolution ( 852x480 ).

[jagabo]

nevermind

[cannibalica]

It is capable of showing most resolutions but it will be downsized to the TVs max resolution ( 852x480 ).

So if I send a 720p or 1080i signal to my TV, the picture quality will not be different from 480p or even worse?

[edDV]

It is capable of showing most resolutions but it will be downsized to the TVs max resolution ( 852x480 ).

So if I send a 720p or 1080i signal to my TV, the picture quality will not be different from 480p or even worse?

That is right. The native screen resolution (852x480 in this case) is what is displayed. Everything coming in gets converted to that resolution.

480i, 480p = 720x480/576
720p = 1280x720
1080i = 1920x1080

Analog is equivalent to approx 352x480 (NTSC) or 352x576 (PAL)
A good comb filter might get slightly higher horizontal resolution (up to ~480).