Direct flights from Portugal with TAP (http://www.flytap.com/) every Friday, returning same day.Additional direct flights from Europe and the US are possible with Royal Air Maroc (http://www.royalairmaroc.com/).
The Daily Air Senegal flight is no more, however TACV Carbo Verde Airlines (http://www.caboverde.com/...) have daily flights from Dakar, Senegal to Bissau every day. The flight time is 75 minutes.
From Ziguinchor, Senegal to Bissau it should take you 3-4 hours by sete-place seven-seat Peugeot or your own car, depending on the border bureaucracy and the ferry in SÃ£o Vicente A bridge is under construction, improving access to Senegal and Gambia markedly. This bridge is completed but won't be open for use until the end of May 2009. Roads are in good conditions. The ferry in SÃ£o Vicente operates approximately from sunrise to sunset, after sunset, you will have to cross in canoa pirogue and change to another vehicle.
From Gambia Serrekunda, count on 7-8 hours if everything goes smooth. If going by sept-place, you'll have to switch in Ziguinchor. The only really bad road in the trip is in Gambia, just before the border to Senegal.
Dakar-Bissau with public transport can be done in one day with a little luck, but you need to leave Dakar early and change vehicle in Ziguinchor.
Other main borderposts include Pirada dirtroad from there to GabÃº to Senegal, and Buruntuma to Guinea-Conakry also via GabÃº.