It's relatively "trivial" to convert from, e.g. PNG to EPS. I'll assume, since you're using Quark, that the concern is more about output resolution than vector vs. raster; Image::Magick, among others, can convert a high-resolution PNG into EPS very nicely. We've used this for printing to filmsetters with very good results (at 1.4 Kdpi). Just be certain to create the PNG with the proper resolution. (Also, I seem to recall that when using GD to create PNG's, the image density ("dpi resolution") was not set correctly, so we had to add a step in the Image::Magick portion to "force" the image density to the correct value.)
If you're looking for vector-only EPS output, there are some PostScript::* modules in CPAN, but the first one that caught my eye (PostScript::Elements) seems woefully undocumented. I'm sure that there is one out there, just search around a bit :-)
