SQL Server 2005 Acting Up (not a valid dbo).

[ayende]

Visual Studio gives me the following two messages whenever I open it:

This database does not have a valid dbo user or you do not have
permissions to impersonate the dbo user, so database diagramming is not
available. Do you want to make yourself the dbo of this database in
order to use database diagramming?

And then:

This database does not have a valid dbo user or you do not have
permissions to impersonate the dbo user, so database diagramming is not
available. Ensure the dbo account is valid and ensure you have
impersonate permission on the dbo account.

I'm administrator on the box, and I dropped and recreated all the
databases, but I can't get it to work.
Any ideas?