I like the 2007 Vanden Plas rims, which are 18 inch x 8 inch. I have a 1995 XJS that I would like to put them on which is currently the 16 inch five spoke rims. Can anyone tell me if this is possible?

 

The best I can determine is the bolt circle is the same, but the centre hub hole is smaller on the 2007, so the wheel won't fit over the hub.
The usual warning here is that 16" is about the biggest wheel you want to use, otherwise the cars have a tendency to become skittish and tramline at highway speeds. The suspension doesn't like low profile tires.