Can upgrade SQL 6 to SQL 2005?

Yes, we can but !!!!!!!
Migrating from SQL 6 or 6.5 is possible is you have SQL 7.

SQL Server 2005 is capable of running in several “database compatibility modes”, allowing 2000 and 7.0 databases to run within a SQL 2005 instance.  SQL 6 waswhat Microsoft get and 7 was his first version. In order to upgrade to SQL Server 2005 users will need to move from 6 to 7 first then upgrade to SQL 2005. David Campbell  a member of Professional Association for SQL declared in the SQL Magazine explain more about“