A scheme with the hotel location and surroundings of IST is shown in the next picture:

In front of each hotel you will find stairs that lead to the ALAMEDA subway station.
Lisbon subway is organized by colors, Alameda station gives a connection to the red and green lines (cf. diagram).
Downtown station is called Baixa-Chiado, and Oriente station leads to the modern Expo-98/Parque das Nações compound.
Lisbon subway covers only a limited part of the town (it has no connection to the airport).
You may buy a very cheap 1 day pass (check price).

You may find more detailed information on the Hotel A.S. Lisboa at this webpage
Hotel A. S. Lisboa prices for WIOP participants are about 49 Euros(single) / 59 Euros(double) per night.

You may ask more detailed information on the
Residencial Fonte Luminosa (Alameda D. Afonso Henriques, 70 - 6th floor)
Tel:     +351 21 840 4896,  Fax:    +351 21 840 9003, Mail:  fonte_luminosa@netc.pt
Resid. Fonte Luminosa prices for WIOP participants are about 34 Euros(single) / 46 Euros(double) per night.

Fig.1: View of the IST central building
 

Fig.2: View from the IST where you clearly see Hotel AS Lisboa.
 

Fig.3: WIOP-2002 will take place at the Complexo Interdisciplinar building.

Fig.4: Close to the Complexo Interdisciplinar building, you find the
Department of Mathematics (3th, 4th and 5th floors).