Owner of one of those renowned ASUS P5Bs
and I can confirm jmicron trouble is over with the following:
- PCLinuxOS 2007
- Fedora Core 6
- Ubuntu 6.10 (LiveCD only, not the alternative CD)
- Mandriva 2007.1 Cooker
- Sabayon Linux 3.26 and 3.3
- Debian Etch (using the most recent install CD)
Slackware is unlikely to work because it has an older kernel by default; the same goes for Gentoo, although I downloaded a "SmallGentoo" just the other day that was produced precisely to solve the JMicron/Sata issue. I haven't been able to give it a try so I can't confirm anything yet.
As for that motherboard of yours, are you sure it has a JMicron controller? I've been over this with other owners of Intel boards and it's my impression that these are still having serious issues all of their own.