For a "selection" of a person or object as you describe, Aperture is not going to work very well. You can crop (square or rectangle) but no smart or manual selection around a person. Adobe Photoshop will work for what you want . Photoshop CS6 is the newest version. Adobe's version numbers are kind of confusing - I have Photoshop CS5 on my Mac Pro (Lion 10.7.4) that shows version 12.0.4 x64. I would recommend Adobe Elements 10 if your version of Photoshop doesn't work for you - it gives you about 90% of Photoshop at much less $.
Selecting an person or object can be easy or difficult depending on the background and the degree of perfection that you are looking for. There are some good on-line tutorials. Good luck.
No, you do not want to use such an ancient version - even if it did work. Far superior cheap or free editing is available from modern non-Adobe image editing applications.
Every digital photog needs good conversance with a modern image editor. Aperture excels at images management, it is only marginally an image editor.
Instead I recommend GIMP (free) or Pixelmator. Full hugely-expensive Photoshop used to be the only real choice but only full-time pros need it today. Folks like me still use it mostly because it is what we know. Photoshop Elements is less competent and less expensive than full PS but IMO GIMP and Pixelmator are better value.
All image editors have a learning curve but are worth the effort.
Tasks like "isolating a village priest from his surroundings .. or isolating a football player from the field or pitch" is a challenge for most basic image editing apps, including full PS (however each new PS version does improve). Personally I use KnockOut2 for isolating parts of images even though I own the full Adobe CS5.