In the eyes of what law?
In american law - and probably european too (since these things seem to be pretty global). It wouldnt supprise me if the actual number varied - but I would be shocked if anywhere claimed that anything with less than 75% market share was legally defined as a monopoly

This may not occur to you but no court in the world could enforce a world-wide split up of Micro$oft. The worst-case scenario is that they'd split in the US and carry on as per usual elsewhere.

Wrong
The US governemt could without a doubt split up microsoft - worldwide. It is an american company which has a world wide presence, but its still american.
I am unaware of the capabilities of the EU over whether they could enforce a split order, but there is no doubt that the US government could enforce a global split (for example, if non-US divisions broke off to form their own "united" company, they would not be able to use/sell the code developed by the US company on any other terms than those of normal resellers) - However, they could certainly prevent microsoft from trading in europe unless they split, which would effectively kill the company if they did not split

btw, that article is really quite old - I could possibly have found a better source of information
A judge DID order the split up of microsoft (Judge Jackson) but that was overturned on appeal because of some out-of-work comments that jackson made which indicated that he was biased against microsoft; but the original conviction was upheld, just the punishment was sent back for re-negotiations

A second judge (cant remember her name) was tasked to decide on the punishment, then bush got elected and the DoJ accepted/proposed a very much watered down rememdy with microsoft - which the 2nd judge accepted

Feel free to check out the official (but difficult to read) DoJ website...
http://www.usdoj.gov/atr/cases/ms_index.htm

Actually, the overview is a pretty reasonable starter for all anti trust cases (not MS specific)

At the end of the day I don't care either way
Fair enough - everyone can choose whether they find the current situation acceptible or not wink

because I don't intend on spending my life stressing about one man controlling the computer world.
Also fair enough - who cares if billy is gonna charge everyone £150 for windows? Sure, we HAVE to buy it because everyone else uses it, and he's just doing it in the name of compatibility, but so what? £300 isnt too much for an operating system - if he wants to charge £400, we still have to pay because its a monopoly which we cannot get out of due to the compatibility requirement...

The only difference is that microsoft know that if they charged that much then everyone would realise that their monopoly is BAD for the consumer

No matter how much Gates is hated by anti Micro$oft people he's not gunna go away, so it's best just to think about something else.

True, Gates wont go away for a long time - and very few anti microsoft people hate the man gates, their just jealous of his money - no, they hate the illegal practices that he and his company used to squash competition, 'cause competition is good - right?