FreeBSD6 on PowerEdge 4200

[Enrique Ayesta Perojo]

Hello, i'm trying to install FreeBSD6 on an old PowerEdge 4200. But i cannot 
even get to sysinstall, when it's booting from the cd it gets to a point 
where the system reboots, these are the messages i can see on the console:

...
amr0: <LSILogic MegaRAID 1.51> port 0xf480-0xf4ff irq 9 at device 19.0 on pci0
amr0: busmaster bit not set, enabling
amr0: polled command timeout
amr0: polled command timeout
panic: amr: slot 0 busy?

Uptime: 1s
Automatic reboot in 15 seconds - press a key on the console to abort
...

It happens with FreeBSD5.4 and FreeBSD6.0 install disks, but not with a 
FreeBSD4.10 disc, any clue on what could be happening?

Thanks a lot