I'm personally a fan of -- and use almost exclusively -- Premiere and After Effects, but the Elements is a relatively bare boned version of the CS variants. It's pretty easy to learn, though.
Of those three, I'd lean towards Pinnacle. The current layout is very similar to the high end Avid editing software (which is not surprising, since Avid owned Pinnacle until very recently) but Corel redid a lot of the coding and made it a lot faster. It's also very capable of doing chroma keying, even if the lighting on the green/blue screen isn't uniform. It's also actually pretty novice friendly. Considering it's what my dad uses to edit his home movies and he still double clicks internet links, that should be saying something.
If you're willing to wait for a sale and are willing to spend a bit more money, try to find a store selling Premiere CS5.1 or 6. It's well worth the premium over any of the mentioned software. But if you're just looking to do relatively basic editing, you can't go wrong with Pinnacle Ultimate. Just don't buy the lesser variants of Pinnacle - they cut out a lot of very useful features.
Edit: Does your friend currently use any editing software on his Mac? Certain programs can still export workload files that are compatible with other programs, though mainly for rough cuts. Things like transitions and certain effects aren't translatable between different software.