questions about fields(again)

[sebastian___]

I'm doing music videos, special effects and commercials for 5 years. I've read many articles about TV fields and I've read them many times. But unfortunatelly, I still have many questions. I understand the whole theory with how a image is made of fields, lower field, upper field ..and so on. And in the past I even had problems because I used some wrong settings ex: upper instead of lower or reverse. But now, it seems that it doesn't matter. And that conflicts with everything that I learn. If I use for example Adobe Premiere, what setting do I have to choose when capture (by firewire). Or when I export ? Because it seems that no matter what setting I choose, it's just fine. The motion and quality is the same. I could choose a regular DV pal setting like lower field when I capture, and lower field when I export. Or I can choose the "no fields" setting. And it's just the same. Same results. How can that be possible ? And sometimes I choose "no fields" option and I do all sorts of speed change and it's ok. But sometimes it's not ok at all. Sometimes If I do a speed change at edit, I get a very strange motion like alternating between an older frame and a newer frame. And in that case I have to change to "lower field" setting. But that change I do only in the project. I still do all the captures with "no fields" setting.
Usually I have to change the fields setting in the project, when I change the camera.

And another question is, how I export a progressive material ? Shot progressive or made with computer animation ?

Question 3 : Is it possible that some cameras(PAL) export movies in 25fps interlaced mode and others in 50fps interlaced modes ? If yes, maybe I found some answer with some weird stuff regard fields coming from a camera or another....