To be honest old chap, I'd take or send it back or, at the very least, contact the supplier. It's three weeks old and it may take ages to get it working to your satisfaction.

However, I get the impression you don't want to do that, so try a few things before succumbing to the inevitable :-

1. Use Aero Glass with a standard Vista wallpaper and monitor the freezing.
2. If 1 above still freezes try a lower screen size, say, 1280 x 800.
3. Try other ‘default’ settings that you may have changed.
4. As it’s only three weeks old, perhaps you could go back to an earlier point via system restore, or even reset it to factory settings.

Finally, for the third time of asking “Have you downloaded all the Vista fixes from Microsoft“?