Everyone once in a while may need to launch an application on their Mac in 32-bit mode. This is a very easy process, but can throw you for a loop if you don't know where to go. The most common reason to do this is if you are running a more recent version of your graphics program but still rely on some of your older plugins that only show up in 32-bit applications. If you are running an older plugin and its not showing up in your graphics program, this is a good thing to try.
Open your finder and go to your Applications folder and select the program you wish to open in 32bit mode. In this case its going to be Photoshop CS5.
Once you have found the application you wish to open, right click (or control click) on the application to bring up the context menu. On this menu you will choose the "Get Info" option.
Once you click on the the "Get Info" option another window will show up with information about the selected program. This is where you will choose the option to open in 32-bit mode. Remember that once you choose this option this program will continue to open in 32-bit mode until you uncheck this box.
Remember as mentioned before, if you need to turn this off you will need to follow the same process you did to turn it on and it will remain running in 32-bit mode until you turn it off.