Before installing this pre-release software, you should review the associated readme files for system requirements and a list of known issues:

Visual Studio 11 Beta Readme
.NET Framework 4.5 Beta Readme
Team Foundation Server Beta Readme
Compatibility with previous releases
.NET 4.5 is an in-place update of .NET 4 and provides very high app compatibility for all .NET 4 scenarios
You can install and use Visual Studio 11 Beta alongside Visual Studio 2010
Visual Studio 11 Team Foundation Server Beta requires 64-bit versions of server operating systems when installing on Windows Server (see Visual Studio 11 Team Foundation Server Beta system requirements)
Upgrade paths
When following the supported upgrade paths, your Visual Studio source, solution, and project files will continue to work; however, you should expect to make some changes to sources. While we cannot guarantee binary compatibility between releases, we will do our best to document significant changes to assist you with updates.

Supported:
Upgrade from .NET 4.5 Developer Preview to Beta
Upgrade from .NET 4.5 Beta to Release (RTM)
Upgrade from Visual Studio 11 Beta & .NET 4.5 Beta to Release Candidate
Upgrade from Visual Studio 11 Beta & .NET 4.5 Release Candidate to Release (RTM)
Not supported:
Upgrade from Visual Studio 11 Developer Preview to Beta; however, you can install Visual Studio 11 Beta after uninstalling Visual Studio 11 Developer Preview
Upgrade from Visual Studio 11 Beta to Release (RTM)
Note: For C++ desktop applications, redistribution of Microsoft Visual C++ files is not supported with Visual Studio 11 Beta, so static linking to the runtime is required.

Carrying assets forward
All data in Visual Studio 11 Team Foundation Server Beta (work items, source files, tests and test results, builds, and warehouse data) will be carried forward when following supported upgrade paths. Even when following supported upgrade paths, you should take adequate measures to back up and protect your data prior to upgrading to a new release.