The CTP4 for SQL Server 2008 has been released as a Virtual Image to install directly on your Virtual server installation. This download comes as a pre-configured VHD. This allows you to trial SQL Server 2008 CTP 4 in a virtual environment. You need to download the 4 files for this CTP4, earlier it used to be inform via Connect site but now this is directly available from MS Downloads ....(
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Read the complete post at http://sqlserver-qa.net/blogs/sql2008/archive/2007/09/07/1935.aspx