Most troffs can be ``coerced'' into including PostScript figures. The best approach is a configuration that takes EPS PostScript and can automatically scale it, or tell troff how big the picture is. Groff and DWB 3 have this built in.
psfig is an add-on EPS inclusion handler that can add this capability to other versions of troff, provided that a compatible PostScript driver is used (Psroff 3.0 for ditroff or CAT troff, Transcript for ditroff). See the comp.text FAQ for more detail.