Following the instructions here:
http://merb.rubyforge.org/files/README.html
I executed:
svn co http://svn.devjavu.com/merb/trunk merb
cd merb
rake install
The command output was:
C:\InstantRails?\merb>rake install
(in C:/InstantRails/merb)
rake package
(in C:/InstantRails/merb)
Successfully built RubyGem?
Name: merb
Version: 0.4.1
File: merb-0.4.1.gem
sudo gem install pkg/merb-0.4.1 --no-rdoc --no-ri
rake aborted!
Command failed with status (0): [sudo gem install pkg/merb-0.4.1 --no-rdoc ...]
C:/InstantRails/merb/rakefile:76
(See full trace by running task with --trace)
Removing the "sudo" and commenting out the chmod command (which would work in Cygwin but I'm using the Vista command shell) allowed the install to succeed.