OK. I just went through the Japanese-language manual, & I think I've got it.
Go into the Movie shooting menu, as shown below:
Scroll through this menu until you see this text. (It says "EX Telecon" in Japanese.):
Turn it [ON].
When it's on, you should see its icon on the screen (#33...
You're doing it wrong.
Here's the full resolution:
http://img98.imageshack.us/img98/4656/25pdeinterlaced.jpg
I don't have any editing software with me, so I simply deinterlaced it in VLC using X mode. It then plays back just as if it were a 25P file.
EDIT:
No, I was wrong, svecher is right...