Microsoft SQL Server 2008 CTP 4 has been released 20070831 (yes that is ISO format)
So I have been sleeping for the last couple of days and missed this. Connect didn't email me either ;-(
This download comes as a pre-configured VHD. This allows you to trial SQL Server 2008 CTP 4 in a virtual environment.
Get it here: http://www.microsoft.com/downloads/details.aspx?familyid=6a39affa-db6e-48a9-82e4-4efd6705f4a6&displaylang=en&tm