In Lisbon, I usually stay ar Residencial Estrela do Saldanha Avda. Republica, 17 (Metro Saldanha, Duque de Avila exit). Co-owner Carlos Ferreira speaks English and has a website.
A weekend just allows you time for the Lisbon area: you could daytrip to Sintra and/or Estoril. Public transportation in Lisbon is very good. You definitely want to spend time in Belem and maybe at the Expo'98 site (Parque dos Naciaoes). If you happen to be in Lisbon the first Saturday of a month, the ladies at Nossa Senhora da Fatima Cathedral in Lisbon have a full day charter bus to Fatima (if that's your 'thing').
For dining, I like the Portugalia (brewery) restaurants: one at Colombo Shopping Mall, one about 400m west of Cais do Sodre Ferry Terminal (Quayside), and the original on Almirante Reis, a few blocks from Metro Alameda.
There's also the old chalkboard outside Tavern menu in commercial areas. Tapas at most bars include Croquetas de Bacalao (I love 'em!).