I think the most important thing to do is to make sure AHCI is enabled. I'm using a 1U Supermicro SuperServer that has a 4-slot hot swap backplane and built-in SATA controller on the motherboard ("pretend" hardware RAID, aka BIOS-aware software RAID, but doesn't do much good for linux, since for linux it's both unnecessary and probably slower than linux's sw raid). I'll give you more precise information tomorrow.

BTW, it should be possible to do software RAID expansion under linux. Apparently, it's a new feature under the 2.6.17 kernel:
http://scotgate.org/2006/07/03/growi...5-array-mdadm/

Here's a wiki:
http://linux-raid.osdl.org/index.php/Growing

Here's a howto guide for MythTV:
http://www.mythtv.org/wiki/RAID#Soft..._5_with_XFS.29