"How can I damage 89C51??"

A large hammer is usually quite effective! ;-)

"4. How can I generate micro-second intervals from within windows, in order to program the microcontroller?"

As has been noted before, MS Windows is not a real-time operating system; it isn't designed to do this sort of thing!
You'd have to get into the world of low-level device drivers.
Could you do it in MS-DOS (real MS-DOS - not a Windows DOS-box) instead?