I just wanted to mention a great new site for programmers called Stack Overflow that just went into public beta.
It's a mix of a technical question forum and a wiki, focused on software development and architecture, and has a few "hooks" that pull you in -- as you ask and answer questions, you get "reputation", which unlocks more privileges (such as editing the wiki). You also earn "badges" for doing things like asking a popular question or giving the best answer.
It ends up being really addictive and also valuable, people are rushing to provide the best answer the fastest to questions you ask, so if you have a focused technical question, it's a great way to get multiple answers fast. I asked a question on Word 2007 automation, and had two great answers with code samples within 15 minutes.
Anyhow, I say check it out.
Ok, I've been bitten by this twice now, so here is the error and solution:
Error:
TITLE: Microsoft SQL Server Management Studio
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Database diagram support objects cannot be installed because this database does not have a valid owner. To continue, first use the Files page of the Database Properties dialog box or the ALTER AUTHORIZATION statement to set the database owner to a valid login, then add the database diagram support objects.
Solution:
In my case, it's because my domain login is set as the database owner but I am working remotely. My PC can't validate my login against the domain, so SQL Server errors out with "invalid owner".
The easy solution is to change ownership of the database to sa, using sp_changedbowner.