I did some further research, and I see you are manually embedding the imagevue2.swf. Why not use the SWFObject javascript as in the Imagevue examples, which handles cross-browser integration properly, including flashvars?
I checked the source code for your gallery, and you have flashvars only in the <embed> tag. I believe Internet Explorer uses the <object> tag, so you would need to add flashvars there also. See this:
http://helpx.adobe.com/flash/kb/pass-va ... a_SWF_file
This is why it would be easier to use the SWFObject JS which allows you to set parameters once, and then it applies them cross-browser.