many thanks to you guys... I now have a vibration-free super-smooth car again!!!
I found a Pirelli Performance Centre not too far away, and went there with your comments... turns out my wheels were supplied with the wrong nuts, no spigot rings, and had been balanced appalingly!! (they showed me one, which was actually BETTER balanced once they'ed REMOVED the weights that had been put on it!! yikes!)
...so it cost me a fair bit (new nuts, rings, full 'positional-balance' on studs).. but it worked!! yipeeeee! The guy was also very helpful and explained the whole lot, and obviously knew what he was talking about, and actually cared, which most tyre-fitting places just don't seem to do.
so, a big thankyou to you all again!!