I used the Word 2007 equation editor for a recent paper. I like the editor because it supports TeX-like commands. Unfortunately some journals do not support Word 2007 equations. PLoS Biology suggest saving down as Word 2003 and recreating the equations manually. Argh, that sounds like a terrible way to spend an afternoon.
Thankfully, MathType can convert Word 2007 equations to MathType equations. It’s hard to find any information on this on their website but the latest MathType has a Convert Equations option (above). The conversion is not perfect (it had trouble with overbars) but over all it’s serviceable. Certainly less painful than retyping the equations.
Update: Once your equations are in MathType format, you will need to use the MathType interface. To use TeX commands such \alpha, go into Preferences > Workspace Preferences… and tick Allow TeX language entry. You can then enter TeX commands in the main interface by typing \, the TeX command, then hitting the Return Key.