Thank you, in the meanwhile I found out it is rather easy to patch setenv.cmd to work (only patch the path in a single line).
However then I have to pass the target system, which is not detected automatically and no matter what target is choses it displays afterwards:
Targeting Windows XP x86 DEBUG

************************************************** ********************************
WARNING: The VC++ Compiler Toolset is not using Windows SDK v7.0. To use Windows

SDK v7.0 use 'WindowsSdkVer.exe -version:v7.0', or alternatively you can pass the
'/useenv' switch to vcbuild.exe to use the Windows SDK v7.0 on a per project basis.
************************************************** ********************************
does this mean that SDK 7 is not useful for VC 2005 anyway?
Do I have to install the old SDK 6.1 ?