This can only be done in IE. Also be careful about hiding the cursor, it is how people navigate and also how they know where the mouse is. If you were to hide the cursor completely on the page everywhere that you currently are using the black one, many folks would be lost even with that swirling colored ball effect that you have for the cursor's general location. Now, no script is really needed to use custom cursors in IE, it is really just style. So, I would suggest getting rid of the existing cursor script/style that you are using and in the image tag of the images where you want to hide the cursor do this:
HTML Code:
<img src="whatever.jpg" style="cursor:url('blank.cur'), crosshair;" />
Use blank.cur (right click on the link and choose Save Target As).
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