I'm by no means an economist but I've studied it for the past year and 3 months as an A-Level in my grammar school, although doing badly at AS, I do business studies as well, meaning I do know a bit about markets and monopoly structure, so here's my call:
Firstly, look at this:
http://en.wikipedia.org/wiki/Monopoly. Read it through.
In Business, a legal monopoly in the UK is a company that has a market share of over 25%, although in Economics I believe it to be a market of many buyers, but only one seller. Meaning depending on the product's elasticity it can change price and demand should only decrease a little if inelastic, or none at all if it's perfectly inelastic.
I'm reckoning you should wack some diagrams in, like the monopoly one, and explain how although Apple sell to
x% of the market (go find figures) that they don't actually control the market, and if they did have total economic defined monopoly power then talk about profit max and whether you think Apple operate where Marginal Cost = Average Revenue (i think

).
Then ermm. Let me think.
I googled and got this:
http://www.theregister.co.uk/2004/10/12/ipod_us_share/ which quotes
"Apple iPod grabs 82% US retail market share" which is very very high. I don't think that Apple has anywhere near that for it's computer products, possible 5-10%? I couldn't be sure without looking.
Anyway.
Hope that points you in the right direction. Worst comes to worst, tell your teacher it was hard, write some crap that's worth a few words, and then they'll explain it to you next lesson
Nick.