As far as I am aware the trademark is for the name and not really the extension, so it could still be classed as an infingement depending on what you choose to do with it.
It does seem possible for more than one person to be granted a trademark for the same name as long as it is for a totally different use (see below).
Trademarks can be hard to get your head around and there does seem to be alot of confusion about them.
An example would be the word Inca - Some Live examples are below
Word Mark INCA
Goods and Services IC 025. US 022 039. G & S: Belts ; Caps ; Cleats for attachment to sports shoes; Clothing, namely, wrap-arounds; Footwear not for sports; Hoods ; Infant and toddler one piece clothing; Jerseys ; Leather belts ; Mufflers ; Shifts ; Short sets ; Shoulder wraps ; Sport coats; Sport shirts; Sports bra; Sports jackets; Sports jerseys and breeches for sports; Sports overuniforms; Sports shirts; Sports shirts with short sleeves; Ties ; Tops ; Wraps. FIRST USE: 20000305. FIRST USE IN COMMERCE: 20000305
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Word Mark INCA
Goods and Services IC 029. US 046. G & S: shortening and edible oils
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Word Mark INCA
Goods and Services IC 009. US 021 023 026 036 038. G & S: communications software for wireless mobile devices. FIRST USE: 20060100. FIRST USE IN COMMERCE: 20060100
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Word Mark INCA
Goods and Services IC 009. US 021 023 026 036 038. G & S: Electronic components; namely integrated circuits for digital telephones. FIRST USE: 20010228. FIRST USE IN COMMERCE: 20010228
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Word Mark INCA
Goods and Services IC 009. US 021 023 026 036 038. G & S: SOUND RECORDING CARRIERS, NAMELY, DISCS, COMPACT DISKS, LASER DISKS, AUDIO CASSETTES, DIGITAL VERSATILE DISKS, NUMERICAL DISKS, AND MINI-DISKS; PRE-RECORDED FILMS, DISKS, COMPACT DISKS, LASER DISKS, AUDIO CASSETTES, DIGITAL VERSATILE DISKS, NUMERICAL DISKS, MINI-DISKS, ALL FEATURING POPULAR MUSIC EXCLUDING ANDEAN MUSIC AND DANCE
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................Plus quiet a few more...There are also variations like Inca Gold - Inca Inox - Inca Mama - Inca Inchi and more.
This is not a legal statement - just an observation 
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kubativity said:
So if i happen to find hotmail.org is available, than you're saying i could register it and put up a site about, say, some sexy emails I've been getting or something like that?
I don't think it is as clear cut as that - I would'nt try it with something as obvious as that. There is probably a big difference from using a generic word that is Trademarked compared to using someones Brand that is Trademarked.
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