Thanks Dave, worked so far. As always I get these messages when installing something
Warnung: RPMDB wurde außerhalb von yum verändert.
...
Rpmdb checksum is invalid: dCDPT(pkg checksums)
But fortunately yum+rpm is operational.
For others following daves proposal, please remind that yum bootstrap creates
PATH=C:\usr\sbin;C:\usr\bin;... in path statement.