The July CTP of SQL Server 2008 is now out! There are quite a few additions on this CTP from that of the June one. Refer this link to see these improvements. And click here to get to the CTP home. To download the CTP you would need to get yourself registered at Microsoft Connect.
It's best recommended to try out this CTP on a separate machine, since there are a few issues you may run into if you have or have had previous versions of SQL Server installed. Refer the readme located on the CTP home for further installation issues.
Gogula G. Aryalingam (MVP - SQL Server)