Mobo upgrade issue

Hi,

Got a Asus K8s-MX board with 754 pin 3000 AMD and have a single Seagate SATA 120GB drive. got 512MB Ram, 256 MB 6600 Nvidia on AGP (YES AGP NOT PCI-E) and a 5.1 Soundblaster Live!
have a situation leading to possible change of system here:
if a second hdd of same type is hooked up, the bios detects it, the OS sees it, formats it but thats it. if i copy some files, try to mirror raid it, locks up. swapped sata cables, power cables, ports, etc but same result. the OS is XP Pro SP2.
the second drive will work by itself if i try loading a OS to it but not together. bios has been updated and all so at complete loss. the drive has been replaced twice already but to no avail. HELP!!! power supply is a 400Watt which works fine ( I hope).
considering upgrade of the proc and mobo anyway in a week or so. the current chipset looks like a SiS and the new mobo looking at is a A8V Deluxe from Asus. it appears to have a Via chipset so will I have to reload the OS? the OS was losded thru a SiS driver and now if chipset is changed..... what would be suggested? if i have to reload the OS, how do i make a Via Drivers floppy as despite popular suggestions of SP2 detecting SATA, it does not and needs a driver floppy to be used. so.... what can anyone suggest some resolution to this?