say for example someone has the domain xxx.com registerd. the domain is not being used and there is no sign of it being put to use in the future. now say u register xxx.net, after xxx.com has been registed. u develop xxx.net into a succesful website and trademark the name "xxx." can u legally take xxx.com from the owner? or can they hold out and request an insane amount of money?

I would think the one who had possession first would be able to keep it as long as they wanted. You would have developed it knowing someone else had it first. Also what a person may request to sell for, and what they would actually take after it is put on the table may be very different.

Obtaining a trademark after the xxx.com was registered makes things more difficult, although nothing is impossible if you can establish 'common law' trademark: usage of the name in interstate commerce at a time prior to the registration of xxx.com. Makes sense? :D

also in the example, "xxx" is not a common dictionary word.