Firstly you need to understand the route.
There is no Metro at Lisbon Airport yet.
You would need to get a cab from Lisbon Airport to Gare Oriente Station.
This would take between 10 and 15 minutes dependent on time of day.
From there you would have to get a train to Porto Campanha Station.
Transit time about 2hrs 40 mins to 2hrs 50mins.
From Porto Campanha you would then need to get the Metro to Estadio de Dragão - The Porto Stadium.which is the terminus and four stations down on the ABC and E lines
To be safe and allow for problems you therefore need to allow 4 to 4.5 hours for the trip.
For information on the Porto Metro see:
http://www.metrodoporto.pt/pagegen.asp?SYS_PAGE_ID=873878
For information on the train times Lisbon to Porto go to my blog at
http://barlaventostravelblog.blogspot.com/
Scroll down in he right hand panel till you find the section:
Algarve & Portugal - Travel Transport Links
You will find a link entitled:
"Porto - Lisbon - Porto Train Timetable"
Click on it and you will be able to download the current timetable in pdf format from Portuguese Railways for the Lisbon - Coimbra - Porto service.
Hope this helps.
