The issue I had with trying to get SQL Server 2005 SP1 to coexist with SQLExpress SP1 was that the "default" database instance, which in this case is SQL Server 2005 Enterprise SP1, wouldn't appear in SQL Management Studio when browsing for network servers. I'm not sure if this is a bug or some kinda "by design" thing that exists for backward compatability but tweaking the install order seems to have fixed the issue.
The install order is as follows:
- Install SQL Server 2005 Enterprise on the default instance
- Install SQL Server 2005 SP1 on the default instance
- Install SQLExpress SP1 on the "SQLExpress" instance
You will end up with SQL Enterprise on the "default" (also known as "MSSQLSERVER") instance and SQLExpress on the "SQLEXPRESS" instance.
I don't know if this is an weird scenario but it seems like it should be fairly common. I personally use this box as a "staging" server for websites that are in development and having SQLExpress on the box allows us to test sites without having to alter connect strings.
I suspect the issue appeared because I was installing SQLExpress SP1 before SQL Server 2005 Enterprise and since there's no slipstreamed SQL Server 2005 with SP1 SKU, I'm guessing the lack of SP1 on the default instance was confusing the "SQL Browser" service. I don't know why installing SP1 didn't fix the issue. The magic is all in the install-order I suppose.
Of course I haven't actually rebooted the machine yet. If the issue reappears after rebooting, this qualifies as a bug, right?