@ DarkGoth: If you are using the Windows Live Messenger 9 RC (a.k.a. version 14.0 - not
the Beta), then you can't do anything with the downloaded file.
It's a registry file which adds the DUIDebug value in order to make Messenger Beta load the old layout files. This registry value however no longer has any effect
on the Windows Live Messenger 9 RC version. There's no way to make the new version load those old layout files, simply because that registry value was used for debugging and because those old layout files are most likely already removed from the RC.
Since we can no longer use the old style of changing the layouts of Messenger through XML (UIFILE), we have to wait for the new layout format to be reverse-engineered, documented and implemented in Plus! until we can make skins for this new Messenger version. This is also the reason why Plus! is currently only partially compatible with this version: it loads and hooks into Messenger, but it can't modify the windows to add buttons such as the Plus! button and text formatting tools.
For the time being, either downgrade to version 8.5 or version 9.0 Beta in order to use Plus!, or simply stay with the new version and wait patiently...