FreeBSD 5.0 hard disk geometry problem at install

[Robert Downes]

I am attempting to install FreeBSD 5.0 (from a CD supplied with FreeBSD 
Unleashed, second edition - good book) onto my P4 system. The first 
drive is a 40Gb Fujitsu ATA-100 which Windows XP Pro is sitting on. The 
second disk is a 14Gb Western Digital ATA-66 which I intend to devote to 
FreeBSD if it ever wants to accept me as a host.

However, Sysinstall says the probed reading of the geometry of ad0 is 
obviously wrong and sets it to something else. When I set it to what my 
BIOS says [19623/16/255], it tells me this is obviously wrong too. When 
I tell it what pfdisk reports it as [4981/254/63], sysinstall is happy 
with the values and carries on. The installation seems to go fine, but 
when I try to boot my machine, Boot Manager offers me:

F1: ??
F5: disk 1

If I hit F5 I am offered

F1: disk 0
F5: freebsd

I hit F5 and then get a boot: prompt from FreeBSD telling me that 
/boot/loader and /kernel are not available.

Sometimes a bad install like this will kill XP's ability to load 
properly. I got right up to the login screen before XP froze, the first 
time. But booting the XP installation CD and running fixmbr (?) to reset 
the MBR, then going all through the install seems to restore XP without 
loss of personal files. Other times, selecting ?? at the Boot Manager 
will allow Windows XP to run perfectly fine. (I'm doing so now.)

So I don't know what to try next. I even swapped the IDE cables around 
in my box because originally the HDDs were on the secondary channel, but 
I still get the same problem, so that cannot have been the cause.

Any suggestions? I've already ordered new hardware to dedicate to 
FreeBSD, and I'm dreading getting the same problem there.
---
Bob