Since last couple of months, I was trying installing Rails-3 on my Windows PC.
When I heard, that Rails-3 requires ruby-1.8.7 or higher, I instantly removed Ruby-1.8.6 and all its components and installed 1.8.7 from the fresh point.
I was happy, as my new system has Rails-3 now… Wow, what else I need?
But later, I found that my few of my old applications, which requires ruby-1.8.6 have stopped working. WTH!! Can’t it work with Ruby-1.8.7 now? With the investigation, I observed that, there were few libraries which were specific to 1.8.6 version and are not in 1.8.7 now. Some of them, I restored from 186 to 187 but were not compatible. Urrrgghhh!!! I am disappointed 
Now, I need some sort of version Manager, which will handle multiple version of Ruby. From here my search starts!!
After searching a lot on Google, and suggested by one of my friend, I found ‘pik‘.
Short Intro about Pik: Pik is a version manager for Ruby. You can handle/install multiple versions of Ruby and switch between them easily.
Basic Requirement: You must have atleast one version of Ruby, up and running on Windows.
Installation: ‘pik’ comes as a gem. To install pik, follow these steps:
Dependencies:
> my current plateform: ruby-1.8.6. From the command prompt, type:
gem install pik
> After the successful installation of pik, type:
pik_install C:\tools
> Add this to your Path Environmental variables
My Computer > Right Click > Properties > Advanced System Settings > Environmental Variables > Path
Once you’re done. Open a new command prompt and type:
pik list
It will add the current version of ruby into the list.
Now what’s so special about pik? How it can handle the multiple versions? To see that in action, in command prompt, type:
pik install ruby 1.8.7
and this will start downloading and once downloaded it will install 1.8.7, under:
C:\Users\PC-name\.pik\rubies\Ruby-187-p302
Awesome!! isn’t it?
pik list
It will show you the current version of ruby and the other ones.
pik use 187
Will use now ruby-187. Don’t believe me? 
Then type:
ruby -v
I am super excited now 
I want to install Ruby-1.9.2 now. Afraid? Still hesitate? Don’t be, just follow the instructions…
From the command window, type:
pik install ruby 1.9.2
Heights of happiness… It is installing 1.9.2 now!!
Path will remain the same, i.e:
C:\Users\PC-Name\.pik\rubies\Ruby-192p302
Do a pik list now and you’ll see:
<image comes here />
Now, I am running multiple versions of Ruby on my Windows m/c and I can select any version by:
pik use 187
gem install rails --include-dependencies
rails s -p 4000
and can perform numerous operations… Yuppy!!!!
Here comes the another pain. Few days back I thought to work with Rhodes. The Mobile Framework for Ruby.
To install it, I went through the Rhodes website and followed the tutorials. I did:
pik use 187
gem install rhodes
I got make error Why windows won’t work like the Linux does and why do we need to troubleshootC-compiler problems?
Another day I spent to look around for a solution and finally came up with Devkit.
Short Intro about Devkit: Devkit is a windows executable program, which creates native extensions for your Ruby gems, which uses C-complier.
Installation: Download the Devkit (Development Kit) from Ruby installer website. After downloading, extract it to:
C:\devkit
After extraction, open your command, go inside C:\devkit prompt and type:
ruby dk.rb init
This will create the config.yml inside C:/devkit. Now you need to define all the Ruby versions inside that file, so that devkit will create native extensions for them. To do that, open that file and at the end of it, write these lines:
- C:\ruby
- C:\Users\PC-name\.pik\rubies\Ruby-187-p330
- C:\Users\PC-name\.pik\rubies\Ruby-192-p0
Once done save it and from the command prompt, type:
ruby dk.rb install
and you should see something like this:
Awesome, easy steps, isn’t it? Now, what else you’re looking for? Go ahead, install any gem for any version of ruby without any hesitations 
Please let me know if you’re stuck or need any help. Good comments will always motivate me to write more and more and help the Ruby Community keep growing.
References taken from:
PUNEET PANDEY's WEBLOG 