Confused about NTSC with 4:3 & 16:9

I know the differences between 4:3 and 16:9 ratios and how either or get translated onto either size display, but what I'm not understanding is what NTSC has to do with the two different aspect ratios. ie:

If I have a DVD that is formatted at a widescreen (16:9) format and send it to a widescreen display that is currently set to display at a 16:9 ratio, is there any converting happening between the DVD player and Display unit?

Virtually all modern 16:9 displays are HD displays with much higher resolution than DVD, so the picture is being scaled up. Only the earliest plasmas (circa 1998) were EDTVs (853x480) and involve no scaling.

But since you phrase your question with regards to conversion (which I'm taking to mean NTSC vs PAL), no conversion (as such) is involved.

Using a similar example above but using a 4:3 formatted source from the DVD to the display that is still set to display at 16:9 ratio, would the display be converting the 4:3 source to fit the 16:9, making things zoomed or stretched?

This is dependent on the settings of the components in question. Some DVD players can be set to adjust the signal from 16:9 to 4:3 depending on how the material is encoded. (Note that this functionality is not part of the DVD specification, so it's available in only a few players.)

Otherwise, the display can be manually adjusted to manipulate the picture (stretch, zoom, crop, etc)

The final question is, even though the DVD says it's formatted in widescreen (16:9), is the actual signal itself a typical 4:3 (NTSC) signal that is being converted by the display back into a 16:9 image? It's this broadcast NTSC standard of a 4:3 ratio that is confusing when trying to determine how a 16:9 format is being transfered via hardwire or broadcast carrier....

Anamorphic encoding - the heart of DVDs being able to do widescreen - means that the picture is stored as what might be seen as a 4:3 frame (a 720x480 image) but the image is not meant to be displayed in that ratio. It's actually distorted on disc and is 'corrected' by your DVD player depending on how you've set the player's Aspect Ratio (sometimes labeled as TV Shape). With a typical 4:3 setting, lines of resolution are thrown out and letterboxing is added. With the 16:9 setting, the image is stretched out (to what would be 853x480) but no letterboxing is added, and all the resolution is maintained.

But, to the best of my knowledge, anamorphic encoding/transmission is not allowed in NTSC broadcasts. So when a film is being shown on (standard-definition) AMC, it's broadcast with the letterboxing.

Or am I not understanding what you're asking?