problems installing 6.1-RELEASE on Dell PowerEdge 1855

[FBSD]

I'm trying to do a fresh install of FreeBSD 6.1-RELEASE on a new
Dell PowerEdge 1855 blade server.  The hardware notes for 6.1 say
the Dell PERC 4/IM SCSI raid controller is supported by the amr
driver.  The problem I'm having is that the kernel on the install cd
is trying to load the mpt driver, which sees the controller and then
fails to load with a timeout error.  How do I install FreeBSD with
just the amr driver and not the mpt driver?