5.2.1-RC2 Panics

I've just got a new Asus A7N8X-E Deluxe motherboard on which I've 
installed FreeBSD 5.2.1-RC2. I had run FreeBsd-STABLE for several years 
on another motherboard, so I thought it was time to upgrade.

I have two P-ATA discs mirrored using vinum, including the root. Apart 
from that it's all per the basic install so far, except that I have to 
boot with no ACPI in order to actually finish booting 
(hint.acpi.0.disabled=1 in /boot/loader.conf). With ACPI the system 
will not boot.

My problem is that when I try to rebuild the kernel, I get panics. I've 
had two different kinds so far:

panic: lockmgr:  locking against myself
cpuid = 0;

syncing disks, buffers remaining... 3839 3839 panic: free locked buf
cpuid = 0;

I also got the following this morning when trying to buildworld:

Fatal trap 12: page fault while in kernel mode

The instruction pointer was 0x8:0xc061l05b and I'm running 5.2.1-RC2 
GENERIC, so maybe it'll be useful for someone.

Does anyone have any ideas as to why it's so unstable? I'm running the 
same on a Compaq Deskpro (except no vinum) and all is well. Is it a 
problem with the nForce-2 chipset or maybe vinum? I've never run vinum 
before as my old motherboard had a promise RAID controller on board.

The problem seems to be load related as it also happens after cvsup-ing 
when doing a portsdb -Uu.