[Tutor] trouble installing library

[Lolo Lolo]

im not sure if anyone is familiar with virtualenv but im tryng to follow a tutorial that has asked me to install virtualenv. i downloaded it in the form of a tar file and extracted it. There was no .exe file to install. The tutorial asks for me to type this code :

$ virtualenv --no-site-packages gmapenv 
$ cd gmapenv

but i get a few errors. 1st virtualenv isnt a know command, so i put python infront of it and get an import error:

ImportError: No module named virtualenv

Am i installing it correctly? can anyone offer any help? Im on Windows Vista, and i have both python 2 and 3 but i would prefer to use Python 3
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