Thanks to a blog contributor bleedingedge, now I know that there’s a tool for Mac OS that is similar to MouseImp. Meet Smart Scroll http://marcmoini.com/sx_en.html
I figured out why MouseImp works for some IE8 users and does not work for others. The trick is that it’s only possible to use MouseImp in IE7 and IE8 if Protected Mode is disabled in Internet Explorer. Not going into much details on what this mode is and why it is advisable to keep it enabled, here’s how to turn it off: IE8-Tools-Internet Options-Security-Enable Protected Mode (uncheck).