I just found out about the Yahoo UI Reset CSS tool/file and I'm using it on my website. On my machine I have Internet Explorer 7 and Firefox 3.01 and my webpage looks the same on these two browsers. A friend is using Internet Explorer 6 and the page is completely a mess. I have two questions:
If you are not particular about testing in your machine, you could try https://browsershots.org or https://blisk.io. These are free and provide screenshots of your site in various browsers on Linux/Windows/Mac OS/BSD.