Lets say you own cars.us -> 4 us Users cars.com -> 4 everybody in za hoooole world cars.co.uk -> 4 UK users All sites ar parked in /public_html/cars how do you avoid getting penalized by Google while keeping all domains active? Well...the answer might be Robots.php
I think that Google's webmaster tools let you pick which domain is the domain that should show up in Google. Then just redirect people out to the appropriate site based on their location.
Perhaps i've missed it, could you gimme some pointers? IF you are talking about Set preferred domain then i advise you to read http://www.google.com/support/webmasters/bin/answer.py?answer=44231&hl=en , as you can see they allow you to set www. domain.com or domain.com as default site address for those whom dont know to make this redirect (dont mind the language , just check the code)