What is TexTablet?
TexTablet is a really simple (and free!) app that allows you to write equations freehand and insert them into a document. Prerequisites

Details
TexTablet uses Windows 7's inbuilt Maths Input Panel (which is really very powerful btw), and translates the output into maths markup, which it leaves on the system clipboard for you to paste into your doc.
TexTablet actually uses the brilliant XSLT MathML library to convert from MathML to . Actually, you might have noticed, but TexTablet is little more than a nice installer and plumbing for the two pieces of tech. That being said, it is quite useful, so feel free to download it from the link below.
Example
A real world example:
gets translated to:
$f\left(x\right)=\frac{1}{2}\sum _{{p}^{\ast }\in {\Omega }^{\ast }}{\left(I\left(H\left({R}_{ \left(x\right)}\stackrel{^}{R}\right){P}^{\ast }\right){I}^{\ast }\left({P}^{\ast }\right)\right) }^{2}$
and is left on your system clipboard after you hit insert.
Download
Handy Links
googlewave.com!w+h0cGV7DCA