Go to Hyperion's website and download the Prerelease Update #1 - it's a new ISO image that replaces the original prerelease CD. The Radeon driver that shipped with the original prerelease is extremely buggy, and the heatwave effect is a known problem. It's corrected in update #1. Install from that rather than the original CD.
Once that's done you've got a few more things to do before you have an up-to-date OS4. Report back here if you need help going through them.
