Install Python 3
then
pip3 install virtualenv
cd myvirtual_p3
virtualenv.exe myvirtual
Install Python 2.7
then
cd myvirtual_p2
virtualenv -p C:\Python27\python.exe myvirtual
cd myvirtual\Scripts
activate.bat
Install Python 3
then
pip3 install virtualenv
cd myvirtual_p3
virtualenv.exe myvirtual
Install Python 2.7
then
cd myvirtual_p2
virtualenv -p C:\Python27\python.exe myvirtual
cd myvirtual\Scripts
activate.bat