- Download the windows binaries for Ruby 1.8.7 here: http://www.ruby-lang.org/en/downloads/ extract that to wherever you would like, I use c:\ruby. Then put c:\ruby\bin in your PATH environment variable.
- Download the zlib package: http://www.zlib.net/zlib123-dll.zip and extract the zlib1.dll, rename it to zlib.dll and move it into your Windows\System32.