LCBoliou,
The core i7s are quad core cpus with multi threading (= 8 'cpus' in the task manager performance view) and Vista 64bit Premium sees all 8 threads. Most of the reviews of the core i7s I have seen have been run on Vista Premium 64 bit.
As it happens I am running Vista Business 64 bit but I think Premium 64 bit handles the core i7 the same.

The new Intel Quad Core i7 cpus (920,940,965) which are available now are multi threaded. This gives you 8 cores effectively and windows sees them as 8 and so do applications. In Carrara for example you get 8 render tiles and it flies!
Unfortunately the Vue 7 Complete 4 CPU limit means you don't utilise the core i7 fully because it won't use all of the threads which is a real shame.

So if you have, or are thinking of getting, a core i7 system, you may want to go with Infinite although IMHO I think Eon are behind the times here and should remove the cpu limit.