Well, I'm not sure if Equation Editor would work with Pages since it is a Microsoft product and comes with the Office. I might be mistaken but this would seems to be a case of apples and bananas.
On the other hand if you have LaTeX installed in your system and are familiar with it then you might try to use a small and free utility called LaTexit. You can check this explanation to get you started on using equations in Pages.
An alternative way to insert equations into Pages would be to use Grapher utility which is included in the standard OSX install. Check in your Applications > Utilities to find it. Not only this utility allows you to produce graphs but it also allows you to copy the equation in variety forms (PDF,TIFF, ... LaTeX equation) into your document. The program has quite good "Equation Palette" where you could in principle create your equations to be pasted somewhere else.