Earlier versions of MSBuild could be found here: %programfiles(x86)%\\msbuild\\
But for Visual Studio 2017RC the path
Posting this for folks still trying to locate the newest version of msbuild on a machine and fall back to an older one if that is availble instead. I find this snippet of powershell does the trick, which can easily be invoked from a bat file.
Function Find-MsBuild([int] $MaxVersion = 2017)
{
$agentPath = "$Env:programfiles (x86)\Microsoft Visual Studio\2017\BuildTools\MSBuild\15.0\Bin\msbuild.exe"
$devPath = "$Env:programfiles (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin\msbuild.exe"
$proPath = "$Env:programfiles (x86)\Microsoft Visual Studio\2017\Professional\MSBuild\15.0\Bin\msbuild.exe"
$communityPath = "$Env:programfiles (x86)\Microsoft Visual Studio\2017\Community\MSBuild\15.0\Bin\msbuild.exe"
$fallback2015Path = "${Env:ProgramFiles(x86)}\MSBuild\14.0\Bin\MSBuild.exe"
$fallback2013Path = "${Env:ProgramFiles(x86)}\MSBuild\12.0\Bin\MSBuild.exe"
$fallbackPath = "C:\Windows\Microsoft.NET\Framework\v4.0.30319"
If ((2017 -le $MaxVersion) -And (Test-Path $agentPath)) { return $agentPath }
If ((2017 -le $MaxVersion) -And (Test-Path $devPath)) { return $devPath }
If ((2017 -le $MaxVersion) -And (Test-Path $proPath)) { return $proPath }
If ((2017 -le $MaxVersion) -And (Test-Path $communityPath)) { return $communityPath }
If ((2015 -le $MaxVersion) -And (Test-Path $fallback2015Path)) { return $fallback2015Path }
If ((2013 -le $MaxVersion) -And (Test-Path $fallback2013Path)) { return $fallback2013Path }
If (Test-Path $fallbackPath) { return $fallbackPath }
throw "Yikes - Unable to find msbuild"
}
$msbuildPath = Find-MsBuild 2017