Hi,
First of all, sorry for the delayed response. Support crew is on summer vacation thus it causes some delay on answering question on Forum.
Normally image swapping should work on all browsers (even on ie8 or older versions). Because it is directly related to jQuery and it is a very simple event.
Since i am using Mac OS X, i don't have IE9 to test it out. Can you check if it also not working on our Live Demo?
demo.flexiblewebdesign.com/~zoom/
If so, please let me know. I will forward this inquiry to developer guy and have him fix it asap.
Regards.
Support.