Boot hangs at "/bin/sh?", can't see USB keyboard

[Chris Shenton]

I have a borked entry in my /etc/fstab: the box can't find /dev/da4s1
or something at boot.  So it hangs at boot asking me if I want to use
/bin/sh in single user mode.  But when I bang on the USB keyboard,
FreeBSD doesn't hear the keys.

I recall that previous boot menus offered a "boot with USB keyboard"
option, but this is no longer on my FreeBSD-6.1 version built from
cvsup a couple months back. 

Any suggestions how to get it to see the USB keyboard in the boot?
This Dell box doesn't have a non-USB keyboard input. 

If not, any suggestions on how to get it to boot to a point where I
could fix the /etc/fstab?  Only thing I can think of is burn a
bootable FreeBSD disk, boot from it, then mount the hard drive and fix
fstab from that.  

Thanks.