Из 6.5 в 7.0 это делается легко:

Upgrading from an Earlier Version of SQL Server
You can upgrade Microsoft® SQL Server™ version 6.x to SQL Server 7.0 using the SQL Server Upgrade Wizard. The wizard upgrades any or all of your databases, transferring all catalog data, objects, and user data. It also transfers replication settings, SQL Executive settings, and most of the SQL Server 6.x configuration options.

The SQL Server Upgrade Wizard does not support consolidation of databases from multiple SQL Server 6.x installations. If you need to upgrade SQL Server 6.x databases from multiple servers, consolidate all of the SQL Server 6.x databases on one server and then run the wizard to upgrade the consolidated server.

When the upgrade process is complete, two separate installations of SQL Server, including two separate sets of the same data, exist. The SQL Server 6.x and SQL Server 7.0 installations are independent of each other from that point forward.

The SQL Server Upgrade Wizard does not remove SQL Server 6.x from the computer, although it can optionally remove the 6.x devices to save disk space if you are using a tape backup to perform the upgrade. You should leave SQL Server 6.x on the computer until you are sure the upgrade was successful.

А из 7.0 в 2000 думаю ещё легче, а скорее всего из 6.5 в 2000 аналогично.