Well, According to Justin from CartoonSmart.com (I puchased his web design videos) let's say you've got a website with 70 frames in it. The first 20 frames is introduction.
It will play while loading the other 30 frames.

If I have a site with 100 frames for example, and the site contains a welcome text or something in the first frame, then basicaly, while the user will be reading my welcome text on the first frame the rest of them will load, so when he will switch to the other frames they will be already loaded.

If I understood correctly, the site will show up even if not all the frames are loaded, like a movie.

If I use load/unload Movie then a 1mb file will have to redownload itself.
I do use loadMovie and loadVariables for text. Some say (in learnFlash.com) that it's better to have a one-frame site, like you said.

I will post the file the minute I'm done working on my file.