MCE2005 - VGA Refresh Rate

I hope somebody can help me with the following problem which is causing me some frustration!

I am running MCE2005 and have connected my 6800GT to my Pioneer 503MXE via VGA. I am running at 1280 * 768 - the Pioneers native resolution - with a refresh rate of 75Hz to hopefully obtain good PAL and NTSC pictures. I am using the 66.93 version of the nVidia drivers.

If I play a DVD using PowerDVD 6 then everything works beautifully and if I press info on the Pioneer remote then it confirms the refresh rate at 75Hz.

However, when I run the actual Media Center app and it switches to full screen, the refresh rate changes to 60Hz! This is fine for NTSC material but not for PAL.

Is there a seperate setting somewhere to tell MCE2005 what refresh rate to use? I have looked everywhere I can think of but cannot seem to find anything. It appears to be defaulting to the NTSC refresh rate all the time, even when playing a PAL DVD.

The same problem arises whether I use the Cyberlink or nVidia mpeg2 decoders.

Anybody have any ideas? Different graphics card drivers? Some hidden setting somewhere?