So the ocaml dependencies don't seem to be handled very well in MacPorts for some reason. I used to have a problem with ocaml-pcre, and now I have problems with libgnomecanvas. My best suggestion is to take your list of dependencies that were not installed and try to manually install all except some of the key ocaml ports. You can just copy and paste that list to a text editor, remove anything with ocaml in it, and copy it back trying "sudo port install <space separated list of ports>". If any ports continue to fail, try to remove them slowly until things install. Then you can try installing paparazzi-tools again. You may have to try this a few times. I realize this method is very hackish, but there isn't a good way to be able to specify more details about the order in which ports are installed in macports, without using a custom script.
Also, before you try installing more, clean the failed port: "sudo port clean ocaml-pcre"
Hopefully that helps. Post to the list if you have more problems. Also, just a reminder, the gcc-arm-embedded that I have set up on the default port isn't really meant for Snow Leopard. In particular, gdb is compiled with python 2.7 support but that framework isn't default on Snow Leopard. You can either compile from source without python support enabled, or try installing the python 2.7 framework. If you don't plan to do JTAG/SWD debugging or programming on the autopilots, then you don't need to worry about it.