I'm certain I'm not the only one frustrated by the historical differences in rendering of CSS by the different browsers. When IE7 was added into the mix, a whole new set of problems was created. I for one was appalled when an OS update I assumed was another Microsoft security patch actually replaced my IE6 with IE7. The only option I found until recently was a Microsoft 'virtual machine' version of IE 6 which supposedly would run independantly and was a download of almost half a gig! I never did get it to work...

Some serious searching has yielded this gem, which is a free standalone version of several incarnations of IE. Manna from heaven!!
check here
Can't live without it now. Enjoy.