I'm currently using CS5. If I install the trial version of new PS will it overwrite my CS5 installation? I want to be sure that CS5 will not be corrupted so that if I choose not to upgrade from the trial I'll still have a workable version of PS.
You can have more than one version of Photoshop installed. Ensure you don't indicate you want previous versions deleted when you install the new version.
Which version of the OS and how much RAM and spare disk capacity do you have?