Internet Exployer 5.5

I have installed Internet Exployer 5.5 on some of our Gateway GP5-200 machines. When they are in IE5.5 and start scrolling down the page, the computer will lockup. One machine will lock up right away. The other two are able to work with the program for a while before the computer locks up. Any ideas as to why this is happening. IE4.0 works fine with no problems.