Electronics wizard's council please....

[reggie 00]

I've read this a few times trying to aim my Mom in the right direction though she went her own way and seems to be pleased with her purchase.

That's all that really counts

Quick question though. Not knowing all the possible # combo's, but understanding that 1080P is where its at, can you noticeably see a difference between 1080P, 1080i and what ever other numbers are available for HD (I think the TV my Mom purchased is a 720).

The difference you will notice will really depend on the person.
The benefit of a "p" display will be the picture will not appear to have jagged edges. This is most noticed in slower moving objects.

Before 1080p displays we usually used 720p instead of 1080i.

Going from a standard tube TV to a 720p display will definitely look good. And depending on your level of need the cost difference between a 720p and a 1080p may not make sense. Go 720 and take the savings to apply toward a 5.1 system or up converting DVD player.
If you have your sights on a Blu ray player, then you will want to go 1080p.

And is there a starting point in screen size that 1080P (1920x1080) starts at, meaning only available in screen sizes larger than say, 37"?

Depends on the manufacturer. but usually yes

I'm sure my urge to purchase a HDTV will continue to rise as my bank account increases in weight, but for now I'm just trying to research as much now as I can so that I'm not cramming when the time has come. If I were to get one now, I'd be looking for a 37", though I know I'd be happier with something a tad larger.

dont discount DLP displays. New ones now use LEDs and a lot of new tech since they first came out. you can usually get a larger display compared to a Wall hung flat screen.

Also Hitachi is coming out with a 1.5" deep flat screen this year. The 37" is supposed to weight in around 26#.