I am looking for any reference dealing explicitly with Eisenstein series on Siegel space (the simplest case of SP4 is fine). Anything would be welcome, but in particular I'm interested in the Fourier-expansions and constant terms. Another preference is that reference be written in the language of the reals instead of the Adeles, though this isn't so important.
Thanks!
UPDATE: Thanks for the references so far! I should have specified, I am interested mostly in the real analytic Eisenstein series, which are induced from the Borel.