i'd have to actually look it up, but my own common sense tells me you can't trademark your personal name, but you can trademark certain titles. for example, if you sold jars of vaseline and put 'mynock spit' under the name 'star wars,' your business lifespan will be measured in nano-seconds. or maybe 'star wars' is considered a logo, which is definitely trademarkable. titles like 'gone with the wind' are unusual enough, imo, to warrant protection. titles like 'psycho'? nah, too generic, unless you're using the franchise name illegally. just my opinion, of course.
as far as pseudonyms, hm, no, i wouldn't consider t.r. barker a 'fake' name when i'd just be using initials. nicknames... maybe. kinda depends: elizabeth to lizzy? nah. joyce to sissy? sure. basically, again imo, if you use a nickname that's commonly known to everyone, you're hardly fooling anyone, eh?
DBA are good things. however, you don't have to be a corporate entity to be a writer. *however* ~ you do have to have a business license (obtainable easily enough for about $25) if you plan on deducting business expenses like reems of paper, ink, postage (and if you really send a lot of stuff out, maybe a postage metre may be a good thing for you), even the cost of the internet service. check out the restrictions. (for a basic business license, you don't have to pay taxes on things as long as it's for the business. every month you have to send in your tax sheet (easy to fill out, you can do them online if you want) even if you haven't made a red cent. not sure if you would really benefit *that* much from having a license. for my trophy business, most places, even some online places, are strictly for business owners. i doubt there are places specializing in writers' needs where you *have* to have a license, lol, but you never know.)
if they wouldn't let me use 'preyer' as my pseudonym, i'd go for t. r. barker. and they'll never use my picture unless it's a full body shot of me in the nude.