Thanks to Jakob Kruse I now know how to operate RubyGems and gemcutter on windows. Here’s what I did:
1:I downloaded the 1.8.6 ruby installer here
2: I installed gemcutter like this:
gem update --system gem install gemcutter gem tumble gem install jspec
this let me use gemcutter on windows using the current one-click installer 
[...] error I did not understand was probably related to that I needed to update rubygems to 1.3.5. I now know how to use gemcutter from ruby1.8.6 using the oneclick installer [...]