We are recently back from three weeks in Spain (thanks Rick Steves for all the great advice!) and wanted to share some information about getting from Figueres (where the Dali Museum is located) to Cadaques (location of the Dali House). You CAN get from Figueres to Cadaques very easily by bus.
Here is the bus schedule: http://compras.moventis.es/paginas/resultados_trayectos.php
For Origen choose "Figueres". Parada Origen choose "FIGUERES Estacio". Parada Desti choose "CADAQUES Estacio". There you have it, plug in a date and these are the buses you can take to Cadaques from Figueres.
We tried to buy the ticket when we were in Barcelona, at the Barcelona Nord bus station, but for some reason they said they could not sell me a ticket, or that there was no bus from Figueres to Cadaques. You want to buy your ticket in Figueres when you arrive. Assuming you came into Figueres to the Figueres train station, just walk out the front door facing the park in front of the Figueres train station. To your left, directly ahead and also along the park is the Figueres bus station. Ticket sales are inside. You cannot buy this ticket online. It is only a one hour ride, I forget exactly how much it cost but it is cheap compared to taking a taxi.
Speaking of taxis, I did not see a taxi at any time when we were in Figueres. Best to just walk the fifteen minutes to the museum from the bus station. We had no trouble getting our backpacks accepted at the Dali Museum in left luggage. And when you arrrive at the Cadaques bus station, it is an easy 20 minute walk to most locations in the town center from the bus station. Don't bother with a taxi unless you have difficulty walking.
Another small note: if your French is better than your Spanish, it seemed that French was spoken more often both in Cadaques and Figueres than Spanish, as a second language after Catalan.
Happy travels!