Do you mean Photoshop version 5 (1998) or Photoshop CS5 (2010)?
If you mean CS5 then you can download a trial from
Ensure that you follow the Very Important Instructions on that page first otherwise the links will not work.
When you launch the trial, enter your serial number to convert it to a fully licensed version.
Thank you. Yes... It's CS5 that I need. Before I beging... should I uninstall CS6 that I have on here? (I had downloaded the trial version to get me through until I could figure this out.) Also... I know this isn't PS related, but I'm not that computer literate when it comes to MAC. How do I uninstall it, if I need to do that? Thanks for all your help!