Ah, this old chestnut!PCs run Windows as their native OS, if he prefers that without trialling OSX then you probably cant help him. Just like you cant change his football team.
A friend, who knew I used both, once asked me what is the *main* difference (in a single sentence). I answered 'Mac sucks less', he then bought one and I have never had to 'go around and get it going again' for him.
Based on price alone; if I could put OSX onto PCs I would. I do prefer Mac hardware however.
Cheers Paul
