This one works for me using the latest ruby one-click installer (the mingw compiled version). It will not work with the older MS compiled versions of ruby afaik. I have it in C:\Ruby18\lib\ruby\site_ruby\1.8\i386-msvcrt\chipmunk.so. I am not terribly good with compiling things in this fashion so ymmv. Hope this helps.
Edit:
I realize now that the version of ruby I have installed is not the one easily found by searching google for "ruby one-click installer" so here is a link to the version I am using:
http://www.akitaonrails.com/files/ruby_devkit-186-p279.msi and the article discussing its existence:
http://www.akitaonrails.com/2008/7/26/still-playing-with-ruby-on-windows. In any case this chipmunk.so should (theoretically) work for anyone who has the linked version of ruby installed.
Second Edit:
I got to another computer to test out the file on a fresh ruby install and it worked perfectly for me. Here are the steps I took to get it working:
* Install ruby from
http://www.akitaonrails.com/files/ruby_devkit-186-p279.msi (make sure you uninstall any old versions of ruby you might have)
* Add C:\Ruby18\bin to your PATH variable (the installer unfortunately doesn't do this for you)
* Install gosu via gem install gosu --platform=mswin32
* Download chipmunk.so (attached) and throw it in C:\Ruby18\lib\ruby\site_ruby\1.8\i386-msvcrt\
I'm not really sure if that path needs to be exact for the last step but that's where it installed when I compiled it and I don't really know if there is a better place for it so I leave it there and it works. If anyone knows better about the ruby inclusion directory hierarchy and has a better idea where to put it or how this could be packaged up nicely, listen to them instead of me.