Do I fly or take a train between these two and how much is each about.
There are 5 direct EuroCity trains at 7:10 am, 9:10 am, 11:10 am, 3:10 pm, and 5:10 pm to Zurich which take 3 hour, 41 minutes. Advance purchase Smart fares are 22 euro 2nd class. City center to city center, that's about the same as flying and a whole lot cheaper. There is another direct train at 7:10 pm takes 4 hour and 19 minutes.
canddlee2,
Travel by train is by far the easiest and quickest option on that route, as mentioned in the previous reply.
I didn't check the flight options, but keep in mind that with air travel it will be about an hour to get from Milan to MXP, the usual check-in and security hassles (another 2 hours or so), the flight and then getting from the airport into Zürich. That entire process will be more stressful and annoying, as opposed to an easy four hour (or so) trip watching the scenery glide by the window.
Happy travels!
Buy your tickets in advance (about 2 months) on SBB.ch to get a special low fare, around 26-30 CHF.