Environment setup : For PHP developer window for normal windows pc.

Following steps installed drush in my windows 7 PC's & laptop seamlessly. Please ignore 1st two steps if you already have a web-server-stack running in your machine.

1. Install VC11
2. Install XAMPP-5.6-VC11
3. Install GIT
4. Install composer
5. Install drush using compser in git-bash type: composer global require drush/drush
6. in bash - navigate to sites folder
7. check environment by typing following commands in bash one by one

   php --version
   mysql --version
   composer --version
   drush --version

Incase any of the above commands returns error, make sure to update environment variables accordingly.

Make sure that your environment variables have these entries (depending upon your install location & user name)

C:\Users\Admin\AppData\Roaming\Composer\vendor\bin;
C:\Users\Admin\AppData\Roaming\Composer\vendor\drush\drush\;
C:\Program Files\Git\cmd;C:\ProgramData\ComposerSetup\bin;
C:\xampp\mysql\bin;
C:\xampp\php;

8. Finally in sites\defalut\settings.php change the host from localhost to 127.0.0.1

Hope this helps