Would it not be better for you to encourage your students to upgrade to the Firefox browser? The files will probably work well with Firefox and you students will also have a more up-to-date browser on their systems (as well as a more secure browser). Microsoft no longer supports IE v.5.5 (nor Windows 98) and the HotPotatoes developers will not support older versions of their software.
Your students could then browse the net with a newer, faster and supported browser (in their very own language) as well as have access to your HotPot exercices written with the latest HotPot software.
Your students may find Firefox at: http://www.getfirefox.com