Well, I hate to disagree with you, but I've been running the betas since they hit the mirrors and they install fine here.
I will admit to not getting them to work on redhat's latest beta tho.
But they will work on mandrake. After you freshly install (not upgrade) beta4 (choosing developmental group during package selection), do not boot into X until you get the drivers set up. Use the tarballs, and run make as root.
If it still gives you problems, please post all errors and your config file.