Windows 7 comes with a cool accessory called “Math Input Panel”. It’s even cooler if you have a Tablet PC.
After you hit “insert”, you can hit Ctrl-V in applications that supports MathML to paste it. Microsoft Word 2007 supports it. You cannot do it in Powerpoint 2007 though, nor in Equation Editor. You can paste into Word, then copy/paste from Word to Powerpoint and end up with an image, not so nice solution.
MathType is a better version of Equation Editor (30-day trial available). Instead of insert Microsoft Equation 3.0, you can insert MathType Equation. Inside MathType equation editor, you can paste the formula created from “Math Input Panel”.
I heard that Office 2010 worked better with Math Input Panel.