Basic Definition located Here

1) Before I start, you must realize that the terms that I (we/ some) use as Progressive, Pseudo-prog (still interlaced) and Interlaced are only slang terms, used for convenience and simplicity.
2) I will assume that you are checking this on a regular TV-DVD combo and checking 24 fps films transferred to NTSC DVD.

PROGRESSIVE:
(Actually it should be called 24 fps mode)
24 Film frames per sec are recorded in 48 video fields (one film frame on 2 video fields @ alternate lines). The DVD encoding includes instruction (flags) for the DVD player to repeat certain fields to make it 60 fields per sec. When DVD is played, the player will follow these instructions to output a 60 fields per sec NTSC signal. This is and should be the normal way of making NTSC Film DVDs.

To check, if the DVD is encoded like a film, turn on the time indicator and check how many steps are there in one sec using frame advance or step forward button. It should be 24 steps in one sec.
(If you use this method on DEI flashing lightening logo, you will see an example of 30 frames per sec Progressive Digital Video)

INTERLACED (Pseudo-Progressive):
(Actually it should be called ‘60 fields per sec Video Mode; 2-3 pull down avail’)

Those 12 extra fields that I mentioned above are actually repeat recorded on to DVD. The DVD player is not instructed to repeat any field.

If you step forward this kind of DVD, you will see that it takes 30 steps to mark one sec. You will also see that every 5th step, there is no change (except noise) from the previous step. (Some times you will notice that every 6th field is a repeated field, like some EVP DVDs; This happens if 24 fps film has been speed shifted to 25 frames Digital Video or to 50 fields PAL and then converted to NTSC)

I call this Pseudo-prog as most line doublers/ scalers can detect this repeat pattern by comparing pixel to pixel. Once a repeat pattern is detected, it will throw away the repeated fields, re-construct the 24 original film frames. The re-creation is not as good as in the case of Progressive DVD. As we can get the original film frames back, I call it Pseudo-progressive. Also note that DVD had un-necessarily recorded about 25% of video fields.

INTERLACED (Field Averaged):
(Actually it should be called ‘60 fields per sec Video Mode; 2-3 pull down not avail’)

There are no repeated fields. 24 Film frames and 60 video fields per sec maintain their own pace. This way, each video fields contains info from more than one film frame (multi-images in one frame or excessive blurriness). As there is no repeat field, the motion stays at same pace (no 2-3 un-even motion). May be a bloody mess though. I don’t think any routine can recreate the original 24 film frames from this kind of signal.

Obviously, if you do the step count, you will count 30 steps for one sec of the timer and all steps will be distinct.

P.S.
If you are using Power DVD software, use Force Weave option. Progressive DVDs will give you no combing (I have come across 2 or 3 problematic 24 fps DVDs though). Interlaced DVDs will give combing in some/ many/ most steps. If you use Force Bob option in Power DVD, it is the same as checking on Interlaced DVD-TV combo.

Good Luck.

Rana

P.S.
If you followed it so far, let me mention that the obvious disadvantage of watching 2-3 pattern of film frames can be taken care of by displaying each film frame 3 times and using a freq of 72 Hz)