Typing in Formulas

Hi all,
I'm typing a paper using Microsoft WORD and need to type in some statistical formulas. However, I don't know how to do it in word. I need radicals, exponents,division lines, etc.
I'd be thankful if you tell me how to write formulas in Word.
thanks i found it.
however, it doesn't let writing exponents and subscripts.
how can i write say, x raised to the power of 2?
or put a five on top of a radical.
when the equation under the radical is long how can i extend the line of the radical to cover the whole length of the formula?
how can i draw long horizental division lines? underlining doesn't work.