For the testing time of the Win 7 you could use Kaspersky Antivirus 2009 beta, trial runs 90 days, that should be enough, until new versions (RC) ar released. Download link in another Antivir-thread in the forum. It's actually a complete security suite, so no worries about malware. Had some problems with it earlier, but seems to run ok now. Kaspersky Internet Security 8 (2009) ran fine on my previous Win 7 installation, but trial is limited to a month. You might be able to find trial-resetters, that work, would be ok for testing a Windows beta, but later on...
Since I did a clean install of Build 7022 with Kaspersky 2009, I've got some problems downloading with IE8, but for now I can't determine wether it's a IE problem or Kaspersky. The download progress windows come up, but then nothing further happens. can't move, resize or minimize them. And download doesn't start. Any ideas?