Which Emacs build for Windows are you using? The GNU one? EmacsW32, which IIRC may have different icons?)
Actually after quite some time of using Emacs I finally went and simply turned off the toolbar. Given that your productivity in Emacs depends somewhat on you being able to drive it via the keyboard anyway, after a little while the toolbar only takes up screen real estate and you gain a couple of lines of code you can look at instead.
So my advice would be instead of spending time to hunt down an improved icon set I would suggest you add the following line to your .emacs and make use of the additional screen real estate :) :