SSDT CTP4 installs components and dependencies that are incompatible with the Visual Studio 11 Developer Preview. As a result, regardless of installation order, these two products are not supported in a side-by-side scenario.
Any attempt to tweak installations so that both products will coexist on the same machine will leave you in an unsupported configuration. There is no workaround for this situation and it is recommended that these two products be installed in separate environments.
For more information or clarification, please head to our team forum here - http://social.msdn.microsoft.com/Forums/en-US/ssdt/threads.