Microsoft and beta software is a story all by itself. In fact, Microsoft treats beta software very differently than most software companies do. While betas are typically developer-only packages elsewhere, Microsoft betas are a fixed and important part of the software release and marketing process that began with Windows 95 and IE4: Microsoft gave away thousands of Windows 95 Betas in prize drawings back in 1994 and the actual IE4 launch was initiated with the IE4 beta – I still have my beta T-shirt given out at a launch party back then.
Users of Windows XP SP3 who simply install IE8 Beta 2 may actually find the browser being locked into their system without any chance to remove the browser without a full reinstallation of the operative system. According to a Microsoft IEBlog post, this scenario will be in place if you installed Windows XP SP3 after installing IE8 Beta 1 and you now choose to install IE8 Beta 2 on top of Beta 1 - and ignore a window with a warning. Microsoft said that you will be able to install Internet Explorer 8 Beta2, but once installed, you will not be able to uninstall either IE8 or Windows XP SP3 later.
“If you chose to continue, Windows XP SP3 and IE8 Beta2 will become permanent. You will still be able to upgrade to later IE8 builds as they become available, but you won’t be able to uninstall them,”
I believe it wouldn’t hurt either if Microsoft published such issues on its IE8 product page and not just in a blog, which not everyone will read. In the end, it is a beta and it should be treated this way - by users and Microsoft. 
Im one who will be in no hurry to try this one out .
I have attempted to install this beta and been told in the process that my system required an update before I could install IE8 b2 . So I go to win update and get the update, which tells me because I have SP3, I dont need the update >:( and so the roundabout continues.
I use IE8 beta2 on my old 500MHZ PIII running XP Pro SP3 and it works great.
I tried Avir! but it would not run and now its running Avir Antivir quite happily.
As always, no Microsoft beta testing >:(
Only option is formatting and reinstalling your Windows. I couldn’t even use the Restore function or Update. Talking of viruses! >:(