Hello Ziv!
On Windows machines Sibelius has to be told, where the VST-Plugins (like Vienna Ensemble) are located. That can be done in the Playback Devices/Audio Engine Options menu. If you don't remember, where you have installed it, you can do a windows search for the file "Vienna Ensemble.dll".
If you want to load your old scores with the playback configurations you made, you will have to get those xml files you mentioned and the corresponding data folders and put them in the Sibelius 5/Playback Configurations folder.
Best regards,
Andi
Vienna Symphonic Library