Disclaimer: I'm a Ruby-n00b and just trying merb.

Did you get this after trying to
gem install merb
?

...
Successfully installed merb-1.0.12
44 gems installed
Installing ri documentation for diff-lcs-1.1.2...
Installing ri documentation for rspec-1.2.9...
Installing ri documentation for addressable-2.0.2...
Installing ri documentation for data_objects-0.9.12...
Installing ri documentation for dm-core-0.9.11...
Installing ri documentation for dm-migrations-0.9.11...
Installing ri documentation for json_pure-1.1.9...
Installing ri documentation for mime-types-1.16...
Installing ri documentation for thor-0.11.7...
Installing ri documentation for merb-core-1.0.12...
Installing ri documentation for merb_datamapper-1.0.12...
Installing ri documentation for ZenTest-4.1.4...
Installing ri documentation for RubyInline-3.8.3...
Installing ri documentation for ParseTree-3.0.4...
Installing ri documentation for merb-action-args-1.0.12...
Installing ri documentation for merb-assets-1.0.12...
Installing ri documentation for merb-slices-1.0.12...
ERROR:  While executing gem ... (Errno::EINVAL)
    Invalid argument - ./</cdesc-<.yaml

Not sure why that is, but it won't stop merb from working. I went ahead a made a for loop to install the other gems again so they'd get their ri documentation.

for %x in (merb-auth-more merb-auth-slice-password merb-auth merb-cache merb-exceptions highline templater merb-gen haml merb-haml merb-helpers mailfactory merb-mailer merb-param-protection merb-more do_sqlite3 dm-timestamps dm-types dm-aggregates dm-validations randexp dm-sweatshop dm-serializer) do gem install %x

Here's what comes from gem install merb-slices -V --debug

ERROR:  While executing gem ... (Errno::EINVAL)
    Invalid argument - ./</cdesc-<.yaml
        C:/ruby/lib/ruby/gems/1.8/gems/rdoc-2.4.3/lib/rdoc/ri/writer.rb:41:in `initialize'
        C:/ruby/lib/ruby/gems/1.8/gems/rdoc-2.4.3/lib/rdoc/ri/writer.rb:41:in `open'
        C:/ruby/lib/ruby/gems/1.8/gems/rdoc-2.4.3/lib/rdoc/ri/writer.rb:41:in `add_class'
        C:/ruby/lib/ruby/gems/1.8/gems/rdoc-2.4.3/lib/rdoc/generator/ri.rb:226:in `update_or_replace'
        C:/ruby/lib/ruby/gems/1.8/gems/rdoc-2.4.3/lib/rdoc/generator/ri.rb:89:in `generate_class_info'
        C:/ruby/lib/ruby/gems/1.8/gems/rdoc-2.4.3/lib/rdoc/generator/ri.rb:44:in `process_class'
        C:/ruby/lib/ruby/gems/1.8/gems/rdoc-2.4.3/lib/rdoc/generator/ri.rb:39:in `generate'
        C:/ruby/lib/ruby/gems/1.8/gems/rdoc-2.4.3/lib/rdoc/generator/ri.rb:38:in `each'
        C:/ruby/lib/ruby/gems/1.8/gems/rdoc-2.4.3/lib/rdoc/generator/ri.rb:38:in `generate'
        C:/ruby/lib/ruby/gems/1.8/gems/rdoc-2.4.3/lib/rdoc/rdoc.rb:324:in `document'
        C:/ruby/lib/ruby/site_ruby/1.8/rubygems/doc_manager.rb:177:in `run_rdoc'
        C:/ruby/lib/ruby/site_ruby/1.8/rubygems/doc_manager.rb:149:in `install_ri'
        C:/ruby/lib/ruby/site_ruby/1.8/rubygems/doc_manager.rb:109:in `generate_ri'
        C:/ruby/lib/ruby/site_ruby/1.8/rubygems/commands/install_command.rb:144:in `execute'
        C:/ruby/lib/ruby/site_ruby/1.8/rubygems/commands/install_command.rb:143:in `each'
        C:/ruby/lib/ruby/site_ruby/1.8/rubygems/commands/install_command.rb:143:in `execute'
        C:/ruby/lib/ruby/site_ruby/1.8/rubygems/command.rb:257:in `invoke'
        C:/ruby/lib/ruby/site_ruby/1.8/rubygems/command_manager.rb:132:in `process_args'
        C:/ruby/lib/ruby/site_ruby/1.8/rubygems/command_manager.rb:102:in `run'
        C:/ruby/lib/ruby/site_ruby/1.8/rubygems/gem_runner.rb:58:in `run'
        C:/Ruby/bin/gem:21