MS Access 2000 Application - SQL Server
I highly recommend you use an .accdb file, not an .adp file. Support for .adp has been removed since Access 2013.

Migrating will vary depending on the application, but quite often isn't an issue at all. Access has high compatibility between versions, and so has MS SQL server.

You can ask about specific problems here or on Stack Overflow depending on the nature of the problem.