I’ve seen this a couple of times now online so it’s worth blogging about. The Enterprise Edition of SQL Server is not supported on client OS's like Vista, XP, or Windows 7. Developer Edition is supported on the client OS's and allow you to develop with Enterprise features, but Enterprise Edition is only supported on Window Server Installations as per the BOL:
Hardware and Software Requirements for Installing SQL Server 2008
Hardware and Software Requirements for Installing SQL Server 2005
If you want to use the Enterprise Features for development on a client OS, you need Developer Edition, the Enterprise Edition Trial won’t work unless you spin up a Virtual Machine and also install an Trial version of the Windows Server OS, or download the Evaluation VHD from Microsoft that includes the OS and SQL preinstalled for evaluation purposes.