Quick tip. Every single version is available as a portable. So just google <insert version name here> portable torrent.
Bit of advice though. Portable versions are not as stable as full versions and come with problems, especially if you are creating DXs with them. As an example some of the versions I've got will let you draw with the lassoo tool but then jump after about five seconds. Others have issues with monitor calibration when you are darkening images (the colours will bleed into each other) and so on. I released a few layouts when I switched monitors not realising this and they were really bad on other people's rigs. I strongly, strongly suggest spending the time to create a monitor profile and calibrate your monitor.
At least that way if people whine about your layouts you can just upload your colour profile.
I personally have several versions installed. I use a full licensed CS (CS1 so basically PS8) for all of my filters and darkening and lamping, then use CS3 CS4 CS5 and CS6 for the new options they had. I can not use any modern portable version for darkening images as they make the artwork bleed, so for example I will darken it using the brightness and reds will get brighter as everything else darkens.
So be careful basically.