sp_changedbowner:
This feature will be removed in a future version of Microsoft SQL Server. Avoid using this feature in new development work, and plan to modify applications that currently use this feature. Use ALTER AUTHORIZATION instead.
ie, as Gazareth said, ALTER AUTHORIZATION ON <database name> TO <login name>
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability