Assuming that this option still exists in 1.1RC1, you can also change these settings using the pluto webadmin under Wizard/Devices/Media Directors.
Nope. It was removed from the Media Directors page as well.
Having installed RC1
just to verify that 
I found the option to change the UI under Wizard/Devices/Orbiters, the option to change resolution under Wizard/Devices/Media Directors however is indeed gone.
Thanks for the answer.
Thre seem to be a problem with the modelines generated by LMCE, each time I use them my screen goes black. If I swich to generic modes in xorg.conf (1024x768) my screen is readable again. This also is the case of the 640x480 modeline in xorg.conf.pluto.avwizard. It is therefore impossible to run the AVWizard. I have tried to cange xorg.conf.pluto.avwizard manually, but it seems to generate again. My linux knowledge is rather limited so I am stuck. Any ideas?
My TV is a Sony 50" projector LCD wich is connected with VGA (and also DVI to HDMI if I want) to av nvidia 6800 LE.
There is a half finished wiki page on installing the latest video drivers, which also has some instructions on setting up the xorg.conf file by hand, it might have just enough info to get you going:
http://wiki.linuxmce.com/index.php/Display_Drivers