Because UserLand's last release was built with CodeWarrior Pro 4, I've been using a Discover Programming edition of CodeWarrior 4 -- the closest I could find on eBay -- but it appears to lack the Power PC Linker specified as a build target.
I'm guessing I need to upgrade to get more linkers, but until I know for sure, I don't want to spend more on this project than I already have.
Just for fun, because I have a current Codewarrior, I downloaded the MacBird sources and attempted to build it. It actually got a lot closer to building than I'd have expected given its age, but it was also quite clear that it would take a not-inconsiderable amount of work to bring it up to date.
It's disappointing, because I think MacBird's goals are laudable, but if you wish to rewrite MacBird to be cross-platform, may I humbly suggest taking a look at http://www.sourceforge.net/projects/whisper2 to do it in? The good news is that the framework is already cross-platform and has good support for XML; the bad news is that you really would need to buy a copy of Codewarrior Pro 8 to build it.