Voltage this side of the pond is 220/240V.
Check the bottom of the transformer for your laptop. For the past 5 years or so most have been manufactured and supplied with dual voltage 110V/240V transformers. If it showns this on the transformer you should be OK to use it in Portugal.
No come back on me though, if something happens...! If you are not confident get a friendly nerd to check for you.)
You will need a dual round pin european plug adapter to allow you to plug in Portuguese sockets.
See this article for more:
http://goeurope.about.com/cs/electricity/l/bl_electricity.htm
