Internet Explorer 7 beta version uni...

I have installed Internet Explorer 7 beta version over IE 6 version of my OS Windows XP sp2. When I uninstalled it, I was not able to work with my earlier version. Getting no chance to work in the browser, I intended to reinstall it. But message comes that it is installed already. So, now I neither can work with earlier version nor new. I am bounded to work with other browesrs like Opera etc. Some of programs which connected to IE only like Yahoo Messenger give error messages when I start it. The first pop up error message is "The procedure entry point InternetGetSecurityInfoByURLW could not be located in the dynamic link library WININET.dll". Please help what to do now to use any of Microsoft Internet Explorer version properly.