thank you for this hint. That is nearly what I need.
This week the OpenSUSE Build Service, which is similar to thetango but
comes with a complete Software management and a http frontend,
has been released for RHEL/CentOS 5 and became very popular.
I'm now dealing with the buildroot (the minimalistic set
of Software for rebuilding SRPMS) which is generated by obs. Its
dependency resolution on SRPM information is said to work much better.
I have to tune a little bit to make this work right for CentOS source
SRPMS and later for the cross build environment. At this time obs is
able to create complete SuSE binary Distributions entirely from the
SRPMs (requiring the minset (binutils,gcc,python,rpm)).

Brian