I caught a documentary on the issue yesterday on I think it was the science channel. They explained why windows has such security problems in detail. it has to do with trying to connect the new OS to the past OS's. If they made a break as Apple did with OSX from OS9 then theycould make a decent OS, but they won't break away.
I've used Android, Google's portable OS for the G1 phone, and it's niffty. i think Google could do well with Chrome and I think OS software as well as many applicationwill be web based in five years time. I have a friend down here, a software engineer, who has been working on such a plan for 10 years, and has the patterns to make a bundle.