Nonvanishing tadpoles and possible infinities associated in the multiparticle
amplitudes are discussed with regard to the disk and RP2 diagrams of the
Type I' compactification. We find that the infinity cancellation of SO(32)
type I theory extends to this case as well despite the presence of tadpoles
localized in the D-brane world-volume and the orientifold surfaces. Formalism
of string S-matrix generating functional is presented to find a consistent
string background as c-number source function: we find this only treats the
cancellation of the tadpoles in the linearized approximation. Our formalism
automatically provides representation of the string amplitudes on this
background to all orders in α′.Comment: 18 pages, Latex, more references adde