In June 2008 we use Viking Line from Turku (Abo) to Mariehamn, we were with our own car.
There is a ferry from Stockholm to Mariehamn and back to Turku.
I think it's better to rent a car for the whole route.
Have a nice time at Alands, it's a realy nice and beautiful place!
The most common way to travel to Aland from Finland or Sweden is to take a ferry. There are couple of main companies (Silja Line, Viking Line, Eckero Line) which are carrying passengers to Aland. Nowadays ships are big entertaining centres. You can spend your time playing pokies, eating in restaurants, watching bands, participating to karaoke or you can even go the cinema. I chose Viking Line because it was much cheaper than Silja Line. Eckero Line doesn`t operate from Finland to Aland. If you wanna be adventurous and enjoy beautiful scenery you can also use small ferries and take a archipelago route from Finland to Aland by car or bicycle.
Åland and Mariehamn are easily reached by boat. Daily lines from Helsinki And Stockholm arrive to Mariehamn at night. Day ferries from Turku and Stockholm take only up to 6 hours. Ferry from Grisslehamn (Swe) to Eckerö takes 2 hours. You can also drive through islands and use small ferries, and the route is so beatiful!!!