Whenever you install any software or application on your Mac, it is very important to know which version of Operating System you are using. It is quite simple to find
This is how your desktop looks
If you concentrate on top left corner of the screen there is an apple button there click that following drop down menu will appear
Click on "About This Mac" option
A window will appear giving you details of your Mac e.g here the operating system is Mac OS X verion 10.5.6
If you press the "More info button" another window will appear which will give you extremely detailed info
Once you have details of your operating system version, you can easily choose softwares and applications compatible with you Mac.... enjoy !