Hello Norbert,
Villa Savoia is now called "Villa Ada" and has the second largest public park of Rome. You can easily find it on Google Maps, it is a large park near the Parioli, just at the border of the aurelian's walls.
The property was espropriated after the 1946, like many other properties ( I believe this was absolutely unfair, it was their private house). The Villa was left to herself and the park became a public parkin 1957 although the Villa was in very bad conditions and the government didn't care about it.
Now it is the Egyptian Embassy, I suppose the interiors were completely destroyed and stolen (perhaps by the government itself?) as this is quite common here.
After princess Mafalda's marriage with the landgrave of Hesse-Kassel the king donated to her Villa Polissena, which is still property of the Hesse-Kassel Family.
If you browse this forum you'll find a pic of Villa Savoia and queen Helena in her bedroom.
G.C.d.R