There are a few ways to do JT65 on a Mac.
The first is to compile WSJT for OS X, which isn't too simple, but if you are comfortable at the command line, it is not too difficult either. You need to be comfortable compiling programs and running from the command line, and you'll need to buy the latest xcode pack from the App Store. Directions are included when you download the WSJT source code.
The second is to give JT65-HF a try. It is a Windows program (there is also an Ubuntu-linux version...no OS X version (yet!)) but it runs just fine in WINE/Crossover. I use it in Crossover for Mac with great results. It does require a bit of configuration, but works great once it is setup. JT65-HF is a GREAT program in that (unlike WSJT) it is JT65 only, it supports multiple simultaneous decodes, and is extensible with the use of JT-Alert (also runs in Crossover).
You could try running it in a virtual machine (Parallels/Fusion) but I've found some issues with that from time to time.
Lastly, as a last resort, you could use bootcamp to boot into Windows when you want to run it.
I strongly recommend trying it with Crossover. Crossover is the paid version of WINE and the latest version (v11) has some great audio support that makes JT65-HF even easier to run. Feel free to email me at my call @ arrl.net if you want some help getting JT65-HF setup in Crossover.