Not a stupid question at all, but no, with FOP 0.20.5 you still need either JIMI or JAI for PNG support. But it may well be that the next FOP version will support PNG without an additional library. For now, you're stuck, though.
thanks for the quick responce, Jeremias. I'm going to be a bit involved with Fedora documentation project's attempt to build up their toolchain using FOP on GNU Classpath based runtimes, so I'm glad to hear that there is a chance of having PNG work out of the box in the next release.
My initial experiments with Kaffe & FOP a while ago have been encouraging. I am considering spending some time getting FOP to work on gcj, Kaffe and other runtimes, as I'd like to use it to generate man pages for kaffe using kaffe, among other things. I assume HEAD is the best place to start for an interested developer?
cheers, dalibor topic
 And with debian's efforts to get FOP into main.