Accessing attached SQL Server 7.0 database from SQL Server 2008 environment

What connection string would I need to access an attached SQL Server 7 (SP3 version, to be precise) database located within a SQL Server 8.0 environment?

This question is driving my work area bats! If an upgrade is needed (as it may be, apparently an upgrade to SQL Server 2008 is not automatic) then how do we upgrade?