Project files are MSBuild files
In a moment of clarity (and subsequently experimentally confirmed) Visual Studio 2005 project files are MSBuild build files.
I started off looking for a way to generate an equivalent MBBuild build file from a VS project file (.csproj).
This is mostly true, but not always true. Windows Forms application setup files are still ad-hoc syntax files that are not MSBuild friendly.
There’s a MSBuild based add-in for web deployment projects in Visual Studio 2005 available here.