I attached my sanyo plv-z5 beamer to the LinuxMCE, which is a 16:9 beamer. The interface of LinuxMCE is displayed in 16:9 but the dvd movie, which I directly played from the original dvd, was is 4:3 and was squeezed so i had to set my beamer in widescreen mode. In this mode the format of the picture is correct, but the interface of LinuxMCE is not completly visible so this is not a good solution for this problem.
The dvd movie has the 2.35:1 format and has copy protection, so I installed the libdvdcss2 to play it. Maybe this is a part of the problem.