Go to www.moniker.com, run a search on the name and it will show if it is taken or not, if it is taken it will show a "BIG RED X".
Click on the "whois" tab and that will take you to the "who owns the name" search function, run the search and print out the owners information and fire him off a letter asking if the name is for sale!
If the guy will not sell it you can always just register the name with an additional word on it: Land, World, Zone, Store, Portal, you get the idea!
If it is a trademark you can register it but the trademark owner can win it back in a dispute.
If it is a generic name I would just add the words above to it and get the .com version of it!
For example someone may have TABLE.com already but maybe TABLEZONE.com is available 