nvidia video overlay problem

Since I put together a new pc I'm having the following problem. I'm
capturing TV shows with a Terratec Cinergy 600 card with a program called
Fly 2000 TV and using the PICVideo 3 MJPEG codec. This all works fine.
However, when I try to play it back with Media Player 11 via TV out to my
TV, I cannot get it to play full screen. WINDVD 7 gives the same problem.
I'm using an ASUS EN7600GT PCI-E with 256 MB memory in my pc set to clone
mode with the latest forceware drivers (tried also with 8x drivers). When I
use huffyuv as a codec, the same thing happens. When I render the footage to
MPEG2 it plays fine on my tv. Playing DVD disks also works fine on full
screen TV. It looks like the video overlay function does not work correctly
with these files.
My previous pc had an ATI 9600XT which played these files just fine in full
screen using TV out.

My system specs:

Win XP SP2 32bit
Intel DP965LT motherboard
Intel E6700 core 2 duo CPU 2,66
2 Gb DDR2 667 memory
Seagate Barracude 120GB SATA2
Seagate Barracude 320GB SATA2
Asus EN7600GT 256 MB
Plextor PX-760SA DVD drive