on window 7 64 bit system
1) if you want to work with ruby version lesst then ruby 2.0
2) you need to install DevKit 32 bit from http://rubyinstaller.org/downloads/ on window 7 x64 bit
if you want to install ruby 2 or greater version on window 7 so you need to install DevKit 64 bit
with ruby 2 with 64 bit
with DevKit 64 bit on window 7 64 bit system ruby 32 bit will not work
but window 7 64 bit system with Devkit 32 bit and ruby 32 bit will work
this issue will not come