In my opinion, they are not really alike. Sybase (Adaptive Server) would be more like MS SQL Server. Whereas MS Access would be used for small applications with a low number of users, Sybase is a powerful commercial database engine, often used as a backend database to web servers, handling thousands (or more) of users.
I would feel that, if you know Access, you DO NOT know Sybase, but if you're competent in Sybase, you could find your way around access easily enough.
Greg.