Ok, the venue is at Costa Salguero, located in Salguero y Costanera, just by the Rio de la Plata shore. It's a big complex that features several "warehouses" where, usually, the Moonpark Parties take place. But anyway, get a cab and ask the driver to take you to Costa Salguero. He'll take you for sure to the right place.
About the tickets: Ticketek (a company very similar to Ticketmaster) always sell the tickets for this kind of events (and most concerts that take place in Buenos Aires). So all you need to do is go to http://www.ticketek.com.ar, search for the Moonpark menu, and then look where the tickets are being sold. I'm not sure but I think there are several places for you to choose, according to your location.
and that's pretty much it
hope this information is helpful
see ya there!