are you trying to install Movi 4.5? try to uninstall the earlier version of jabber off that PC first. in order to install the new package, make sure you have the administrator privilege (i.e. right click on the Movi .msi file and select run as administrator).
regarding the schema question, when you unzip the Movi downloaded package, you will find the schema file corresponding to the downloaded Movi install file is bundled in the zip file (so you don't know to change or create one).
Normally the installation fails (4.2 and newer) because OpenGL 1.2 isn't available. This is normally fixed by updating your graphic card drivers to the latest version (either from the manufactory home page, or homepage of the notebook. Normally it's always best to go directly to the manufactory homepage, e.g. www.nvidia.com for Nvidia chips etc.).
What kind of computer do you use, and with which graphics card (and driver version)?