There is only one train company/service operating from Lisbon to Porto.
See: http://www.cp.pt
If you are staying in the Baixa Area of Lisbon, catch the train from Stª. Apolonia Station.
If staying elsewhere in Lisbon, catch it from Gare Oriente.
In Porto, leave the train at Porto Campanha.
As regards, Rede Expressos, the Rede Expresso depot in Porto is:
ROD. BEIRA LITORAL-GARAGEM ATLANTICO
RUA ALEXANDRE HERCULANO Nº366
4000 PORTO
Tel.: 222006954
See this article on my blog for map to bus station.
http://bit.ly/aJawrR
