RAID mirror, 6.1 won't boot

[tech at nano.net]

I've got a brand new PC, ASUS P5LD2 motherboard and an Intel P4 3.2 CPU. 
I've installed the i386 version of 6.1 over a dozen times using different 
geometries and different drives and such, I get mixed results, but it won't 
boot. I'm running a RAID mirror on 2 SATA drives. If I have the mirror 
turned on and the second hard drive installed I get "no boot device 
available" or I get a boot prompt complaining that it can't find 
/boot/loader. Right now I just get a "-" that blinks, but no boot and no 
system message that it can't find a boot device and no BSD boot prompt. If 
I remove the second drive the system boots normally! If I put it back in it 
won't boot! BSD sees the RAID controller. Is there any easy way to fix 
this? It seems like it's really close to working and I really want the 
redundancy.....