I Think I Read You Need 9GB To Install Leopard
The Installer will tell you if you have enough room - how much you need.
I did Archive & Install from Panther to Tiger with CS on board and nothing broke at all. If you are out of room on your system hard drive and you need to ask that question, you need to think about moving stuff off that drive. There should always be a buffer of about 10-20GB left on any system HD for the OS to run smoothly.Unless something changed in CS3, I remember that older versions of PS used to break after an archive & install. (They'd tell you to reinstall when you try to launch)
Do you know how much space is required to do an archive & install?
The Installer will tell you if you have enough room - how much you need.