It really depends, it's a complex issue (edited a paper my sister wrote on the topic when she was in law school). IIRC, for a small guy to win a case where he uses an established trademark, he has to show good-faith intent upon registration and a legitimate business or personal use for the name.
So a guy who registers the name "www.ipod.com" with the intent of cashing in on the ipod trademark would probably lose a challenge since the registration was made in bad faith. But a guy who registers the name "www.ipod.name" because he has the nickname "I Pod" might stand a chance of winning.
IIRC, it's been four years since I looked into the subject.