Using virtualenv to install different versions of same package
If you have easy_install, or better yet pip installed, should be as easy as:

easy_install/pip install virtualenv
mkdir django1.2
virtualenv django1.2

This will put the python binary in a bin folder inside the django1.2 folder. Just use that python binary, and you've got a nice little self-contained environment. You can then install easy_install/pip into that environment, and then install django 1.2 as well, and hack away.
Since I have Django 1.1x on my Debian setup - how can I use virtualenv or similar and not have it mess up my system's default django version which in turn would break all my sites?
Detailed instructions or a great tutorial link would very much be appreciated - please don't offer vague advice since I'm still a noob.
Currently I store all my django projects in ~/django-sites and I am using Apache2 + mod_wsgi to deploy.