I installed python 3.3.1 on ubuntu lucid and successfully created a virtualenv as below
virtualenv envpy331 --python=/usr/local/bin/python3.3
virtualenvwrapper now lets you specify the python executable without the path.
So (on OSX at least)mkvirtualenv --python=python3 nameOfEnvironment will suffice.
mkvirtualenv --python=python3 nameOfEnvironment