IE8 Beta is officially launched in the MIX08. And you may download it and try it now. Here is the email from the IE team,
As of 12 pm today, we officially launched IE8 Beta!! Please check out Dean Hachamovich (IE General Manager) in the MIX08 keynote. To download IE8 Beta 1, please click here. Please read the Release notes and the IE8 Readiness Toolkit which will give a detailed description of the features. We would like to introduce to you our feedback form, which allows you to submit bugs directly to the IE team! Before submitting an issue, please search for your bug. If you find your bug, please rate the bug which will give us an idea of how many people have run into the same problem. Please only rate bugs that are important to you. If you do not find your bug, then submit a feedback form with the details of your bug. We have made several updates to the IE8: Technical Beta Program available on connect. Please check it out! Best regards, The IE Team.