It seems that Adobe is following in Apple's footsteps with the limitations to old Macs and Photoshop CS6 they are going to close the door a little more to people with Macs from before 2007-2008.
The latest and greatest creation from Adobe will ask for a Mac with at least two cores (Intel Core 2 Duo or better) and 64 bits, plus Snow Leopard as a minimum operating system (Lion and Mountain Lion will also be logically supported).
If you have an Intel Core Duo (it is not 64 Bits) you will have to settle for using Photoshop CS5, which on the other hand will surely serve you well for what you have to do, but I just in case let you know what is going to happen.
Source | TUAW