Sorry to burst your bubble hw-tph, but this is the exact same board that I use and as long as you compile the module for the promise SATA drivers then it will work. I have no SATA drivers, but during the kernel boot it recognizes both SATA connections.
Linux has had support for RAID for a quite a while, and the 2.6.4 kernel will definately support it.
As for the distro, I highly reccomend using Gentoo. It's only $10 to buy (which includes the two Live CDs and the installation manual) and it's extremely customizable along with being able to fit any application that you need it for, whether it be for a workstation or a server PC. It's free to d/l if you have the bandwidth like I do.
Mandrake is a highly expensive distro, unless you d/l it for free, and runs across a lot of dependencies errors whereas the Portage system in Gentoo will get all the dependencies and compile them before the target package so that you don't have problems.
I have a friend that uses Morphix and he says that it is good as well. I say if you want a good distro with an easy install that's small and doesn't put you through dependency hell then use Morphix. If you want a distro that you can fully customize and which also won't put you through dependency hell then get Gentoo. If you want a lot of headaches then you can use Mandrake, but it really is a pain in the ass sometimes. (Mandrake 9.2 is what caused me to make the switch to Linux, and it gave me a lot of headaches with dependency problems when installing things from the source and from RPM's. Not to mention, Mandrake causes many problems by never giving the kernel sources which are very important.
I don't think that Red Hat's any better when it comes to dependencies either, but it might be. The moral of the story is use Gentoo or Morphix if you want a good time.