Where is this discount ticket office located? Can you only get 1/2 price tix for matinees? Is this available daily?

The TKTS booths are located in Times Square and at the South Street Seaport. You can also get tickets for evening shows, not just matinees. The following link has more information.

Have a great time in The City.

http://www.tdf.org/programs/tkts/

The Times Square booth opens at 10 a.m. for matinee tickets and 3 p.m. for evening performances.

The lines are much shorter (if there even is a line) at the South Street Seaport.

Does one location have a better selection of tickets than the other, or do they both have equal access (via computer, like Ticketmaster)?

The Times Square booth reportedly has a greater supply/availability.
The advantage of the TKTS downtown is that it sells Wednesday and Saturday matinee tickets the day before each of those performance afternoons.

Be aware that the TKTS booths only accept cash or travelers checks-no credit cards. Also are you aware there are a number of websites that sell discount tickets in advance that do take credit cards (and would save you standing on line.)? Playbill.com is one. You register for free & can then see what offers they have.

I belong to both Playbill.com and TheaterMania.com. I'm waiting for either "Cabaret" or "Phantom" discount tix for the week we're going to be there in July, so we can bypass that long TKTS line...

Broadwaybox.com is another good resource, along with Playbill and Theatermania. We got two-for-one (great seats, too) for Cabaret in April.

I work very near to TKTS and the lines really haven't been that bad lately. However, that is during the week. The weekends are another story.

One tip: if you're here on Tuesday, it's one of the best nights to find your show at TKTS.