  We study various conceivable photoproduction reactions in a polarized ep
collider mode of HERA with respect to their sensitivity to the proton's
polarized gluon distribution. A special emphasis is put on the `resolved' part
of the cross sections which in principle opens the possibility to determine for
the first time also the completely unknown parton content of longitudinally
polarized photons. In the very promising case of dijet production we also
investigate the impact of parton showering, hadronization and jet finding on
the parton level results.
