Can I install Unity 3.5 and Unity 4 on the same PC

Hi Guys
I’m now using Unity 4.1.2 but would like to continue using the Unity 3.5.
Can I install the Unity 3.5 and Unity 4.1 on the same PC.
My PC has 2 HD (C / E /), and want to know. if I can make a partition you both versions on the same PC, because I liked the new changes of Unity 4 but I do not want to leave because Unity 3 is easier to work with.
What do I do?

I install a version then rename the installation folder from ‘Unity’ to ‘Unity 4.1’ then install other versions then rename them too.
This is on Mac OSX, I don’t know if this works on Windows.

Yes, you can install Multiple versions, however they cannot be running at the same time.

ENSURE THE VERSIONS ARE INSTALLED IN DIFFERENT DIRECTORIES, UNDER DIFFERENT NAMES.

This will be the case for both Windows and Mac