The conference will take place at Conference Center of Instituto Superior Técnico (IST). The Conference Center is building number 2, in this map of IST. IST (Lisbon Technical University) is located in Av. Rovisco Pais, 1000 Lisboa. It is easily accessible by underground, stations Saldanha or Alameda.
IST, the Holiday Inn Hotel and the IBIS Hotel are easily reachable by a 15 minute cab ride from the airport. You should ask for Hotel Ibis, Saldanha, or Holiday Inn near Instituto Superior Técnico. Reaching the hotel by other forms of public transportation is also possible, but less convenient. There should exist a bus that stops at Saldanha, right next to the Ibis Hotel.
The cab ride should cost no more than 2000$00 (10 Euros). You should pay the amount indicated in the meter. This amount will include a fixed excess for baggage (around 400$00, 2 Euros). Here is a map of Lisbon, with IST marked with a red circle and the three recommended hotels (Holiday Inn, Ibis and Sheraton, in order of increasing distance) marked by green squares. A more detailed map of the area is show here.