Ah, memories, when I installed IE and suddenly Netscape died. Turns out Microsoft replaced a needed DLL with one that had different calls to stop Netscape from working.
How about what MS did to Wordperfect... interupted the Printing routines so that Wordperfect could not print more than two copies at a time... If you wanted 20 copies, you had to invoke PRINT 10 times even though you told it to print 20. Word, of course, had no problems with printing more than 2 copies.
MS continues similar practices today with their software to create webpages... often web pages created with MS's tools check to see if you are using something other than IE and, if its not IE, refuse to work correctly. I can set my Safari user agent to IE6 (which basically says "Hey, I'm Internet Explorer!" to any call that asks) and then pages that don't work suddenly work fine. The only thing that is different is that the offending web page now sees "Internet Explorer" rather than "Safari" is at the other end.