I\'m looking at working on a project which uses C#.NET (sitting on a windows box) as the primary language and PostgreSQL as the backend database (backend is sitting on a linux b
Today most languages/platforms (Java, .NET, PHP, Perl etc.) can work with almost any DBMS (SQL Server, Firebird, MySQL, Oracle, PostgresSQL etc.) so I wouldn't worry for one second. Sure there might be glitches and small problems but no showstopper.
As jalcom suggested you should program against a set of interfaces or at least a set of base classes (DbConnection, DbCommand and so on) to have an easily adaptable application.