Microsoft's Equation Writer converts handwritten mathematical expressions to typeset expressions which can be inserted into MSWord documents. I played with the Equation Writer in January 2010 and found it amusing but not usable.
Now Microsoft's Math Input Panel, which I found under Accessories in Windows 7, is definitely an improvement.
I first tried writing the same equation that had given the Equation Writer so much trouble.
To get the expression into a Word document, I needed to have both the Word document and the Input Panel visible, I clicked on the point of insertion in the Word document, then clicked on "Insert" in the Input Panel.
What might make this worthwhile is that once you insert the expression into a MSWord document, you can use the Equation Tools.
For example, suppose you've input "sin x" using either the Math Input Panel or typed directly into the Equation editor (by first simultaneously pressing the Alt and = keys). Now when you right click on the expression, you get a menu of possible actions.
If you click on Integrate on x:
It's interesting that the constant of integration is included in the result. What's also interesting is that if you type a 1 immediately after the C, right-click to get the menu of options, then select Graph -> Plot in 2D, you get an insertable graph that can first be reformatted and/or display an animation based on varying the constant of integration.
You can also go back and right click on your antiderivative, integrate on x, and type a 2 immediately after your new constant of integration. Now when you ask for a 2D graph, you can run an animation based on either of the two constants.
And yes, you can draw 3D graphs in your Word document. Press the Alt key and the = key simultaneously, type in an expression in two variables (such as sin x + cos y), right click and select Graph -> Plot in 3D.
You can drag the image to a preferred orientation before inserting it into your Word document.
You can also use the "Calculate" option to solve some simple equations or to evaluate/simplify algebraic expressions.