Are you installing Leo to SATA or to IDE now?
If SATA the easiest way is setting the SATA ports as AHCI in the BIOS and Leopard should see the disk without troubles (you wont be able to install a retail XP disk in AHCI mode though).
If its IDE it would be more difficult you would need to know which IDE Controller chipset your motherboard has and check if iAtkos or whatever you are installing has support for it.
It doesnt really matter if the drives are detected in the BIOS or not, if OS X doesnt have the proper driver kexts for the SATA & IDE controllers it wont be able to see your drives.

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AsRock P45TS | C2D E8200 | GeForce 8600GTS
Mac OS X Snow Leopard 10.6.1 + Windows 7 Ultimate 6.1.7600 + Fedora 11