Hi Becky,
I have been having trouble with compiling pd externs for Windows using Codewarrior. Do you know if the same things apply for Windows as you have written below for OSX? I've had good success compiling externs in gcc in Linux, but I had a lot of trouble trying to use gcc in Windows. I think mainly due to issuees related to file storage location and writing makefiles (which I know very little about). But I'm not sure what the cause really was.
What exactly are the problems you are writing about? (compiler errors, linker errors, etc...) I have no access to CW for Windows but i think that generally it should work. The fundamental problem of the OSX CW version that can't link to the monolithic pd application is no issue for Windows where pd is split into two parts anyway. I also found it quite straightforward to use cygwin gcc under Windows. You might want to have a look at the project files of some of my externals in case you are not confused by the fact that these are all using flext. (e.g. flext tutorials, http://www.parasitaere-kapazitaeten.net/ext/flext)
best greetings, Thomas