Unfortunately, the rail line to Amarante was lifted a few years ago.
There are almost hourly bus services during the working week from Amarante bus station to Porto operated by Rodonorte.
Timetable extract here: http://goo.gl/UxGJh
You do not really want to drive into Porto, as parking in the centre is bad, as previously mentioned. If you have to drive in, head around the ring road to somewhere like Praça da Batalha/Casa da Musica and try to find parking in a side-street. A good area is around the Metro Station Carolina Michaelis near Praça da Batalha.
Then use the excellent Metro/Bus service and Shank's pony to get around!
If you want to take the train, drive to somewhere like Caide (about 20 kms away and take the twice hourly service into Porto-Campanha or Porto-São Bento)
